Austria's Dominic Thiem revived his hopes at the ATP World Tour Finals with victory over Frenchman Gael Monfils in London.
Thiem, 23, won 6-3 1-6 6-4 and will go into his final group match against Milos Raonic on Thursday with a chance to reach the semi-finals.
Raonic takes on five-time champion Novak Djokovic in Tuesday's evening session at 20:00 GMT.
Both men have the chance to become the first semi-finalist at the O2 Arena.
More to follow.