Kei Nishikori boosted his hopes of reaching the semi-finals at the ATP World Tour Finals with a battling victory over Tomas Berdych.

After four straight-sets singles matches this was a contest the tournament needed and it was Nishikori who came through 7-5 3-6 6-3 after two hours and 23 minutes.

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The Japanese player had admitted he was ashamed after winning only two games against Novak Djokovic in his opening match, while Berdych was well beaten by Roger Federer.

Nishikori, who reached the semi-finals on his debut last year, claimed the crucial break in the 11th game of the first set and seemed on his way to victory when he led 2-0 in the second.

But Berdych won five games in a row on his way to levelling the match.

Both players had chances in the third set but it was Nishikori who took his, breaking for 5-3 and then serving out the victory.

He is likely to need a repeat against Federer in his final group match on Thursday to progress to the last four.