Federer overcomes gutsy Nishikori at ATP World Tour Finals

Roger Federer emerged as the top player of his group after defeating Japan's Kei Nishikori in a thrilling three-set round-robin contest at the ATP World Tour Finals.

The 17-time Grand Slam champion thwarted Nishikori's fightback and claimed a 7-5, 4-6, 6-4 win over the Japanese in a gruelling contest that lasted two hours and 10 minutes, Sport24 reported.

The Swiss maestro had already secured his 13th Tour Finals semi-final spot after ending Novak Djokovic's three-month, 23-match winning run on Tuesday.

Federer will next face either Andy Murray or Stan Wawrinka in the last four on Saturday.