Roger Federer became the first man to qualify for the semi-finals of the ATP World Tour Finals with victory over David Ferrer.
The six-time champion ensured he will not have to rely on other results with a 6-4 7-6 (7-5) win.
Federer has had two straight-sets wins and plays Juan Martin del Potro in his last Group B match on Saturday.
Del Potro eased past Janko Tipsarevic 6-0 6-4 in Thursday's second singles match.
"I thought the match was great, good intensity," said Federer.
"I definitely needed a good second serve, especially in the first set. I didn't have that many serves in play the way I wanted to - either the rhythm was off a bit or I wasn't pushing enough with the legs, or whatever it might have been.
"But I think also credit to him [Ferrer] for being a great return player, getting back a lot of good returns on good serves."
Asked about his feelings on the ATP World Tour Finals staying at the O2 Arena until 2015, he added: "I've loved everywhere I've played over the years at the World Tour Finals but I think this one is obviously special, because it's in London and the O2 is an amazing venue.
"I'm happy it's going to stay here for the next few years."
Federer, winner of this tournament for the last two years, has made typically serene progress this time and, despite Ferrer's recent winning streak of 11 matches, a head-to-head record of 0-13 suggested he was always likely to struggle against the Swiss star.
The Spaniard needed to take every opportunity that came his way, but failed to capitalise as Federer offered up unforced errors and numerous second serves in the opening stages.
After breaking serve at the first opportunity, Federer faced seven break points across three games before a backhand flew long to let Ferrer back into the set at 3-3.
The fourth seed was scrapping hard to stay in touch but Federer has shown he has an extra gear in their previous meetings, and he found it once again.
A brilliant flurry of forehands saw the Swiss accelerate past Ferrer with a love break in game 10 that secured the set, and the 17-time Grand Slam champion steadily improved his game from then on.
A first-serve percentage that had slumped as low as 34% in the first set hit the mid-60s in the second, helping to fend off two more break points as Ferrer battled to keep his winning streak going.
It came down to a tie-break - only the second between the pair - and Federer's now functioning serve proved the dominant shot as he converted his third match point after one hour and 48 minutes.
Ferrer was left to rue nine missed break points, saying: "I had a lot of chances to break his serve. I couldn't do it.
"When he had one break point against me, he made it. With these players - if I don't take my chance, I don't win the important points - it's very difficult to win these matches."
Ferrer's hopes now rest on his final match against Tipsarevic, but he will be a strong favourite after the Serb was beaten comprehensively by Del Potro in the evening match.
Tipsarevic came into the tournament saying he was not 100% physically and he shows no sign of being able to challenge the irrepressible Ferrer, while Del Potro must take on Federer.