Kei Nishikori gave his hopes of qualifying for the last four of the World Tour Finals a major boost with a 7-5, 3-6, 6-3 victory over Tomas Berdych on Tuesday.
Nishikori went into the match with a 3-1 career lead over Berdych, though the pair had not played since 2012.
Both players lost their Finals group stage opener -- Nishikori to Novak Djokovic and Berdych to Roger Federer, meaning a second defeat for either player would leave their semi-finals hopes hanging by a thread.
Serbian world number one Djokovic plays Swiss third seed Federer in Tuesday's other match in the group. Victory for Djokovic would secure his place in the last four, while a straight sets win would guarantee Federer a semi-finals spot.