Novak Djokovic must have found a time machine in the French mountains back in May - because he's woken up in 2015.
The world number one showed us he is back to his best with a flawless win over John Isner in their opening ATP Finals match. Isner's debut got well and truly ruined...
Thanks for your company and join us again tomorrow.. when Roger Federer is scrapping to stay in the tournament. See you then!
Triumphs, tears and tennis
Test your knowledge in our quiz
BBCCopyright: BBC
Maiden Grand Slam victories, 20th Grand Slam victories, comebacks, meltdowns... 2018 has provided no shortage of talking points.
With the final tournament of the year, the men's ATP finals, looming it is time to look back on the past 12 months.
Before you go to bed, here's one final bit of tennis-related entertainment for you...
London until 2020, but where next?
Seeing a packed O2, it's hard to imagine the ATP Finals being anywhere other than here.
They have been held in London since 2009 and will definitely carry on here until 2020 but the bidding process is already under way for the right to host the season-ending showpiece after that.
"We’ve had 40 letters of interest, the actual official bids closed
last Friday, we’ll whittle it down to a shortlist of probably about five in
mid-December and then we’ll announce in mid-March where we go," ATP executive chairman Chris Kermode told BBC TV earlier on Monday.
"London will be
in the mix for sure because it has now become part of not just the tennis
calendar but part of the sporting calendar.
"What we’ve got to be very careful
of is destroying what built up over 10 years. This isn’t going to be a money-grab
– running to somewhere just for the cash.
"We’ll weigh up everything – it’s about
the city, can we get this amount of people though the gates again? This is the
ATP’s season-ending finale, it’s big
deal for us – we won’t be making that decision lightly.
"We
need to ask the top 15-20 players what they would like to do as well."
Getty ImagesCopyright: Getty Images
Andy Murray won the ATP Finals in London in 2016 - how many more opportunities will he get in this city again?Image caption: Andy Murray won the ATP Finals in London in 2016 - how many more opportunities will he get in this city again?
Ouch!
This must've hurt...
In his doubles match earlier today, French player Nicolas Mahut was so desperate to get back to retrieve a shot that he did not see an advertising board.
Before he knew it, he was on his bottom with both feet in the air, his ears ringing from the huge clattering sound, and with a whole lot of pain written on his face.
Just to rub salt in the wound, he may have noticed it was an advertising board for his own shirt sponsor...
(He and partner Pierre-Hugues Herbert lost 6-4 7-6 (7-3) to Mate Pavic and Oliver Marach)
Getty ImagesCopyright: Getty Images
Tuesday's action
But before we see Djokovic, Zverev, Isner and Cilic back in action at the O2, the other group return tomorrow for their tournament-defining second matches.
All eyes will be on Roger Federer, who must beat Dominic Thiem in the evening session (20:00 GMT) to stay in the tournament. We'll be right here with text and radio commentary for you to follow the drama.
That comes after Kei Nishikori, who beat Federer yesterday, takes on Thiem's conqueror Kevin Anderson with both looking to move a step closer to the semi-finals. You can watch that match on BBC Two and here on the BBC Sport website from 14:00.
Zverev punishes Cilic
Zverev 7-6 (7-5) 7-6 (7-1) Cilic
EPACopyright: EPA
Germany's Alexander Zverev punished Croatian rival Marin Cilic's inability to take his chances and open with a straight-sets win.
Cilic, 30, served for the first set but made three unforced errors and a double fault as Zverev broke back for 5-4.
Zverev, 21, went on to take the tie-break and then fought back from a break down midway through the second set.
Cilic saved a match point at 5-4, but Zverev clinched victory in the breaker.
Djokovic's win sets up a tantalising match against Alexander Zverev on Wednesday...
Post update
Djokovic 6-4 6-3 Isner
Leon Smith
GB Davis Cup captain on 5 live sports extra
Novak Djokovic is as good as ever. It is a privilege to watch that.
What he is doing against one of the best servers in the world, to neutralise him and turn defence into attack, dominating back of the court, it is phenomenal.
He is in a good place, physically and mentally, his timing of the ball is fantastic and he's oozing confidence.
Post update
Djokovic 6-4 6-3 Isner
The problem Isner had though was that Djokovic, unlike most of the American's other opponents, kept getting the ball back into play from those first serves which he was landing.
If you didn't already think Novak was the favourite to win this week (and there weren't many of you) then surely you're backing him now...
Post update
Djokovic 6-4 6-3 Isner
Earlier, I said Isner wasn't playing badly - and here are the stats to prove it...
I'd suggest John Isner felt more like Ethan Hunt tonight than Novak Djokovic did...
Post update
Djokovic 6-4 6-3 Isner
More from Novak Djokovic: "The match was great, obviously.
"I had three breaks of serve of John which is sometimes 'mission impossible' but I managed to be at right place at the right time.
"I held serve well, I backed it up from the baseline, I played very solid and didn't give him many opportunities."
Post update
Djokovic 6-4 6-3 Isner
Novak is stood in front of the mic on the O2 court. "I hope you all enjoyed the match," he starts. They probably would have liked to seen more tennis than they did...
Game, set and match Djokovic
Djokovic 6-4 6-3 Isner
Who is going to stop this guy?
Novak Djokovic shows why he is world number one with a machine-like performance. And fittingly he clinches victory with another wonderful winner.
Getty ImagesCopyright: Getty Images
Post update
Djokovic 6-4 5-3 Isner*
Isner saves the first match point with some raw power that Djokovic reads but can't return.
A big first serve helps him see of the second.
One more to go...
Three match points Djokovic
Djokovic 6-4 5-3 Isner*
Wow. Where did this come from? It's 0-40 in the blink of an eye.
Three match points to Djokovic...
Post update
Djokovic 6-4 5-3 Isner*
Eighteen service points in a row for Djokovic. Another four here would do very nicely...
One comes when Isner drills a forehand wide on Djokovic's second serve. But that remarkable run is ended when a crosscourt Isner backhand can't be retrieved by the Serb...15-15.
A slow second serve with a kick of Shane Warne spin bamboozles Isner... 30-15... but Isner levels again with a Glenn McGrath of a forehand that breaks down Djokovic's defence.
But the world number one refocuses and clinches the hold to move within a game of victory...
Post update
Russell Fuller
BBC tennis correspondent at the O2 in London
The crowd just feel that their night's entertainment might be cut a little bit short here.
Djokovic breaks
*Djokovic 6-4 4-3 Isner
Isner saves the first break point with a smart volley, but can't see off the second as he slaps a forehand into the net.
Djokovic stretches those vocal cords again, screaming his satisfaction to the London crowd.
A set and a break up. A long way back for Isner...
Live Reporting
All times stated are UK
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Getty ImagesCopyright: Getty Images Andy Murray won the ATP Finals in London in 2016 - how many more opportunities will he get in this city again?Image caption: Andy Murray won the ATP Finals in London in 2016 - how many more opportunities will he get in this city again? 
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Latest PostGoodbye!
Novak Djokovic must have found a time machine in the French mountains back in May - because he's woken up in 2015.
The world number one showed us he is back to his best with a flawless win over John Isner in their opening ATP Finals match. Isner's debut got well and truly ruined...
Thanks for your company and join us again tomorrow.. when Roger Federer is scrapping to stay in the tournament. See you then!
Triumphs, tears and tennis
Test your knowledge in our quiz
Maiden Grand Slam victories, 20th Grand Slam victories, comebacks, meltdowns... 2018 has provided no shortage of talking points.
With the final tournament of the year, the men's ATP finals, looming it is time to look back on the past 12 months.
Can you remember the biggest moments of the year?
Take our quiz to find out...
Post update
Before you go to bed, here's one final bit of tennis-related entertainment for you...
London until 2020, but where next?
Seeing a packed O2, it's hard to imagine the ATP Finals being anywhere other than here.
They have been held in London since 2009 and will definitely carry on here until 2020 but the bidding process is already under way for the right to host the season-ending showpiece after that.
"We’ve had 40 letters of interest, the actual official bids closed last Friday, we’ll whittle it down to a shortlist of probably about five in mid-December and then we’ll announce in mid-March where we go," ATP executive chairman Chris Kermode told BBC TV earlier on Monday.
"London will be in the mix for sure because it has now become part of not just the tennis calendar but part of the sporting calendar.
"What we’ve got to be very careful of is destroying what built up over 10 years. This isn’t going to be a money-grab – running to somewhere just for the cash.
"We’ll weigh up everything – it’s about the city, can we get this amount of people though the gates again? This is the ATP’s season-ending finale, it’s big deal for us – we won’t be making that decision lightly.
"We need to ask the top 15-20 players what they would like to do as well."
Ouch!
This must've hurt...
In his doubles match earlier today, French player Nicolas Mahut was so desperate to get back to retrieve a shot that he did not see an advertising board.
Before he knew it, he was on his bottom with both feet in the air, his ears ringing from the huge clattering sound, and with a whole lot of pain written on his face.
Just to rub salt in the wound, he may have noticed it was an advertising board for his own shirt sponsor...
(He and partner Pierre-Hugues Herbert lost 6-4 7-6 (7-3) to Mate Pavic and Oliver Marach)
Tuesday's action
But before we see Djokovic, Zverev, Isner and Cilic back in action at the O2, the other group return tomorrow for their tournament-defining second matches.
All eyes will be on Roger Federer, who must beat Dominic Thiem in the evening session (20:00 GMT) to stay in the tournament. We'll be right here with text and radio commentary for you to follow the drama.
That comes after Kei Nishikori, who beat Federer yesterday, takes on Thiem's conqueror Kevin Anderson with both looking to move a step closer to the semi-finals. You can watch that match on BBC Two and here on the BBC Sport website from 14:00.
Zverev punishes Cilic
Zverev 7-6 (7-5) 7-6 (7-1) Cilic
Germany's Alexander Zverev punished Croatian rival Marin Cilic's inability to take his chances and open with a straight-sets win.
Cilic, 30, served for the first set but made three unforced errors and a double fault as Zverev broke back for 5-4.
Zverev, 21, went on to take the tie-break and then fought back from a break down midway through the second set.
Cilic saved a match point at 5-4, but Zverev clinched victory in the breaker.
Read the full report here
Post update
Djokovic's win sets up a tantalising match against Alexander Zverev on Wednesday...
Post update
Djokovic 6-4 6-3 Isner
Leon Smith
GB Davis Cup captain on 5 live sports extra
Novak Djokovic is as good as ever. It is a privilege to watch that.
What he is doing against one of the best servers in the world, to neutralise him and turn defence into attack, dominating back of the court, it is phenomenal.
He is in a good place, physically and mentally, his timing of the ball is fantastic and he's oozing confidence.
Post update
Djokovic 6-4 6-3 Isner
The problem Isner had though was that Djokovic, unlike most of the American's other opponents, kept getting the ball back into play from those first serves which he was landing.
If you didn't already think Novak was the favourite to win this week (and there weren't many of you) then surely you're backing him now...
Post update
Djokovic 6-4 6-3 Isner
Earlier, I said Isner wasn't playing badly - and here are the stats to prove it...
Mission: Impossible
Djokovic 6-4 6-3 Isner
I'd suggest John Isner felt more like Ethan Hunt tonight than Novak Djokovic did...
Post update
Djokovic 6-4 6-3 Isner
More from Novak Djokovic: "The match was great, obviously.
"I had three breaks of serve of John which is sometimes 'mission impossible' but I managed to be at right place at the right time.
"I held serve well, I backed it up from the baseline, I played very solid and didn't give him many opportunities."
Post update
Djokovic 6-4 6-3 Isner
Novak is stood in front of the mic on the O2 court. "I hope you all enjoyed the match," he starts. They probably would have liked to seen more tennis than they did...
Game, set and match Djokovic
Djokovic 6-4 6-3 Isner
Who is going to stop this guy?
Novak Djokovic shows why he is world number one with a machine-like performance. And fittingly he clinches victory with another wonderful winner.
Post update
Djokovic 6-4 5-3 Isner*
Isner saves the first match point with some raw power that Djokovic reads but can't return.
A big first serve helps him see of the second.
One more to go...
Three match points Djokovic
Djokovic 6-4 5-3 Isner*
Wow. Where did this come from? It's 0-40 in the blink of an eye.
Three match points to Djokovic...
Post update
Djokovic 6-4 5-3 Isner*
Eighteen service points in a row for Djokovic. Another four here would do very nicely...
One comes when Isner drills a forehand wide on Djokovic's second serve. But that remarkable run is ended when a crosscourt Isner backhand can't be retrieved by the Serb...15-15.
A slow second serve with a kick of Shane Warne spin bamboozles Isner... 30-15... but Isner levels again with a Glenn McGrath of a forehand that breaks down Djokovic's defence.
But the world number one refocuses and clinches the hold to move within a game of victory...
Post update
Russell Fuller
BBC tennis correspondent at the O2 in London
The crowd just feel that their night's entertainment might be cut a little bit short here.
Djokovic breaks
*Djokovic 6-4 4-3 Isner
Isner saves the first break point with a smart volley, but can't see off the second as he slaps a forehand into the net.
Djokovic stretches those vocal cords again, screaming his satisfaction to the London crowd.
A set and a break up. A long way back for Isner...