Roger Federer continued his serene progress at the ATP World Tour Finals, beating Mardy Fish in three sets to finish the group stage with a 100% record.
The defending champion recovered from a mid-match wobble to win 6-1 3-6 6-3, extending his unbeaten run to 15 matches and remaining on course for a record sixth season-end title.
With Federer guaranteed top spot in Group B and Fish already eliminated, the pair were contesting a dead rubber - but they put on a fine show for the crowd at London's O2 Arena.
"I've played Mardy a few times and he's always very dangerous," said the Swiss legend. "He takes the ball extremely early, serves great and can get on a roll. I was worried in the third set.
"I thought I was going to lose today but I'm very happy. It's been a great run since the US Open - I've been all round the world but I'm still going strong. Hopefully I can make it a nice weekend."
Federer will now turn his attention to Saturday's semi-final against the runner-up from Group A.
This was the first match of the tournament that had no bearing on either player's qualification chances, but there was still plenty riding on it.
Federer was aiming to keep that winning sequence going and register a 37th career victory in the competition - putting him second on the all-time list behind Ivan Lendl (39).
Fish, meanwhile, hoped to mark his final match of the year and Thanksgiving in his native United States with a first win at this level and only his second in eight meetings with Federer.
But he watched on helplessly as the 16-time Grand Slam champion held to love in a one-minute opening game and followed it up with a break of serve for 2-0.
The hamstring injury that forced Fish to retire from his previous two events was being given an intense work-out, and seven errors to Federer's none told their own story.
He managed to hit straight back in game three but that would prove his only game of the opening set, Federer gracefully crafting two more breaks and a 5-1 lead.
The world number four served out when his opponent netted a backhand and at that point it seemed certain Fish would fall to a crushing defeat.
However, back-to-back aces brought a first service hold of the day, and he rushed Federer into a couple mistakes to grab the momentum in game four.
Federer's usual potency was suddenly nowhere to be seen and Fish twice had chances to snatch the double-break before converting his third set point in game nine.
The noise levels rose several notches as both men emerged for the decider but Federer swiftly regained his focus to ensure it was never a contest.
A classy forehand pass up the line saw him break to 15 and a love hold made it 2-0.
Fish saved another break point to get his name on the board but only managed to pick up four points on Federer's serve in the final set.
A backhand crosscourt pass took Federer to 5-3 and he wrapped up the win with a trademark winner off the same flank.