Austria's Dominic Thiem maintained his hopes of reaching the ATP Finals last four with a straight-set win over Japan's Kei Nishikori in London.
The world number eight, who lost to Kevin Anderson and Roger Federer in straight sets in his previous group matches, won 6-1 6-4.
It means Federer will advance to the semi-finals if he wins a set against Anderson at 20:00 GMT on Thursday.
But if Anderson wins in two sets Thiem could progress with the South African.
More to follow.