Roger Federer will end the year as the world's best tennis player for the fifth time after beating Britain's Andy Murray 3-6, 6-3, 6-1 at the World Tour Finals.
The Swiss still has one match to go to qualify for the semifinals, but the round-robin win in London gives Federer enough points to ensure that Rafael Nadal of Spain - the world number two - won't catch him in overall rankings by year's end.
The top eight players are battling for 1,500 points at the tournament, formerly known as the Masters Cup.
On Tuesday, it was Britain's best against the Swiss. In the opening set things looked difficult for Federer as he struggled to return Murray's 130mph-plus serves. The Scot, who is ranked fifth worldwide, returned almost every shot Federer could send his way.
But by early in the second set Federer had found his form. The world's number one remained cool and consistent while Murray began to slip, missing first serves and sending routine balls into the net.
Federer pounded him with solid forehands and well planned volleys. Murray soon broke and Federer never looked back.
Federer will on Thursday face Argentinian Juan Martin del Potro, who held on to beat Fernando Verdasco of Spain 6-4, 3-6, 7-6 (1).
swissinfo.ch and agencies