Britain's Andy Murray will take on Switzerland's Stan Wawrinka for a place in the last four of the ATP World Tour Finals in London on Friday.
They meet in the last round-robin match at 20:00 GMT, with the winner facing Roger Federer in the semi-finals.
A victory would also guarantee Murray the year-end world number two ranking for the first time.
World number one Novak Djokovic will play 14-time Grand Slam champion Rafael Nadal in Saturday's other semi-final.
Semis within sight again for Murray
Murray will travel to Belgium next week for Great Britain's first Davis Cup final since 1978, but he has yet to reach the London final in five previous attempts at the O2 Arena.