World No.1 Novak Djokovic booked his place in the ATP World Tour Finals last four and dumped out Tomas Berdych following a straight sets victory at the O2 Arena in London.
After a double break in the first set and taking it 6-2, Djokovic survived being set-point down to Berydhc in the second set tie-break, but recovered to pull off a third successive win and top group A.
The two-set win means Andy Murray requires just a set against Jo-Wilfried Tsonga in their match in the evening session, while the Frenchman needs a straight sets win to keep his hopes alive.
Both players knew a straight sets victory would confirm their place in the semi-final, while both Murray and Tsonga would be keeping a watchful eye on proceedings ahead of their match in the late session.
After both players between them conceded just one point from their opening service games, Djokovic created three break points straight away, but Berdych found two necessary first serves and then benefitted from a long back hand by the Serbian.
But wayward forehand on deuce allowed the No.1 seed another chance to break, which he duly took as Berdych netted a backhand return.
The Czech almost surged back into the contest in the very next game, as Djokovic miscued a forehand, but two errors from Berdych allowed the Australia Open champion to escape.
Among the ten unforced errors from Berdych in the first set saw a long forehand after an energy-sapping rally hand Djokovic another chance to break, and yet another lapse confirmed the double break.
Djokovic was then able to serve out the set to take it 6-2, to confirm his place in the semi-final, and leave Berdych sweating over his continued involvement.
And the No.5 seed looked down and out after the third game of second set, spraying a forehand long to gift Djokovic a set and a break lead.
But in stark contrast to the first set, Berydch rallied to break back for 2-2 in the second and give his continued participation in the end of season's finals a much-needed boost.
As Berdych's first serve percentage rapidly improved, so did his competitiveness in a match he now had to take the next two sets in and despite missing an opportunity to break to the ninth game at 15-30, he took the game to a tie-break.
Leading 5-1 at the changeover, it appeared a formality for Berdych to secure a third set, but inexplicably, he netted consecutively, first on set point after a darting Djokovic return, and then as the 2008 champion hung in the match.
And Djokovic duly served out at the first chance of asking to secure a third successive win, and dump Berdych out of the tournament.