Roger Federer beats dogged Kei Nishikori in three sets at the ATP World Tour Finals in London

Roger Federer took on Kei Nishikori in the group stages of the World Tour Finals in London and the first set was a tight affair.

Nishikori serving to tie the contest at 6-6 somehow managed to lose this 18-shot rally.

He didn't recover and Federer took the set 7-5.

After battling back from 4-1 down in the second set Nishikori forced an uncharacteristic error out of the World number three at 30-30.

And another at 30-40 to give the Japanese the break and he went on to tie the match at one set all.

Nishikori battled back again to 4-4 after trailing 4-1 but Federer broke the World number eight's serve to lead 5-4 bringing up match point with a sublime cross court backhand.

And after two hours and 10 minutes the 17 time Grand-Slam champion sent down a thundering smash to maintain his unbeaten record and win 7-5, 4-6, 6-4.