Defending champion Roger Federer defeated David Ferrer for the 14th successive time to book his place in the semi-finals of the Barclays ATP World Tour Finals in London.
The second seed still has a final Group B match to come against Juan Martin Del Potro on Saturday but this 6-4 7-6 (7/5) victory was his second straight-sets win of the tournament and means he cannot be denied a spot in the last four.
Ferrer went into the clash on an 11-match winning streak but he had managed only three sets in his previous meetings with Federer compared to 27 for his opponent and again came out second best.
Federer is looking for his third straight title at the O2 Arena and he made a great start, winning the first three games.
That did not tell the whole story, though, as he fought off six break points, and they were back level after Ferrer finally took his eighth chance.
The 30-year-old Spaniard has had the season of his life, winning more titles and more matches than anyone else on the ATP Tour.
He was pushing Federer, who was making quite a few errors but, as he so often does, the world number two found another gear when he needed it to break to love and secure the opening set.
Ferrer had another opening at the start of the second set but could not take it, Federer saving two more break points.
The set was very tight and Ferrer stayed with his opponent all the way until the tie-break, but an error on the sixth point proved crucial.
Federer had been immaculate on serve and took his third match point when a Ferrer return dropped long to become the first singles player through to the semis.