Shanghai Masters: Novak Djokovic and Roger Federer knocked out in quarter-finals
Novak Djokovic and Roger Federer have been knocked out of the Shanghai Masters in the quarter-finals.
World number one and defending champion Djokovic was beaten by sixth seed Stefanos Tsitsipas, who came from a set down to win 3-6 7-5 6-3.
Alexander Zverev beat second seed Federer 6-3 6-7 (7-9) 6-3.
Tsitsipas will play Daniil Medvedev - who defeated Fabio Fognini - in the semi-finals while Zverev will face Matteo Berrettini.
Italy's Berrettini beat Dominic Thiem, of Austria, 7-6 (10-8) 6-4.
Greek 21-year-old Tsitsipas lost the opening three games in seven minutes to Djokovic, a four-time champion in Shanghai.
"It's the best comeback that I have ever had probably," he said.
"It was a very difficult victory mentally too. I wasn't really thinking that long term that I have to win two sets."
Victory confirms Tsitsipas' debut at next month's ATP Finals in London and also marks the first time he has recorded a win over the current world number one.
Djokovic - who won the Japan Open last week - had never previously failed to make the semi-finals in Shanghai.
He now trails Rafael Nadal by 1,280 points in the battle for year-end world number one.
"He had the high-quality tennis and he played very well after his serve," the 32-year-old Serb said of world number seven Tsitsipas.
"He was backing up his serve with really good and aggressive first shots in the rally.
"I didn't make him defend enough. I just gave him enough time to really dictate the play from back of the court and he deserved to win."
Frustrated Federer handed rare penalty
World number three Federer was handed a point penalty in his defeat by 22-year-old German Zverev after he twice hit the ball out of the court in anger.
The Swiss, 38, saved five match points against the world number six in the second set but became engaged in a continuing argument with the chair umpire.
He was deducted a point at 3-0 down in the deciding set.
"[I'm] finally starting to kind of play the way I should play, really. I was playing really defensive the whole year, and not with a lot of confidence," said Zverev.
"He will always find a way. He will always make it tricky for you like he did today with me, and you always got to play your best tennis to have a chance.
"I knew if I kept playing the way I played the first two sets, I was going to have a chance in the third as well."