LONDON (AP) Kei Nishikori improved his chances of finishing the season as the No. 3-ranked player, beating U.S. Open champion Stan Wawrinka 6-2, 6-3 Monday at the ATP finals.
Currently ranked fifth, the Japanese player managed to break Wawrinka twice in each set and start his round-robin group play with a victory.
Wawrinka is ranked No. 3 in the world, but he, Nishikori and Milos Raonic all have a chance to finish the season one spot behind Andy Murray and Novak Djokovic.
Murray will face Marin Cilic later Monday at the O2 Arena, taking the court as the No. 1-ranked player for the first time.
Djokovic can still overtake Murray and finish atop the rankings depending on this week's results.