Kei Nishikori breathed new life into his ATP World Tour Finals ambitions after a thrilling three-set win over Tomas Berdych at the O2 Arena in London. The former US Open finalist produced the goods at key moments and clinched a 7-5 3-6 6-3 victory.
Nishikori looked on-course for a comfortable win in two sets after winning five straight games in taking the opening set and grabbing an early break in the second. Berdych had other ideas, however, producing a five-game streak of his own to claw his way back into the contest and take the game to a third set for the first time in the singles competition.
Both players were locked at a set-all and 3-3 in the decider but as Berdych faded physically Nishikori took full advantage to claim his first round-robin win. The result means any win for Novak Djokovic over Roger Federer will see him reach the semi-final, while a two-set victory for the Swiss player will see him progress with a match to spare.
Despite still being in the middle of the round robin stage, the knock-out stage came a day early for both Berdych and Nishikori after their straight sets losses in their opening matches. A second straight defeat would have all but signalled the end of their campaign in London, yet with a 5-0 record in his second match in the format's history it was Berdych who would start as the marginal favourite.
Nishikori had reached the semi-final on his tour finals debut in 2014 and came into the contest with the better head-to-head record, though the pair had been kept apart for three years despite constantly being around the top 10. In the opening exchanges, neither player gave much away on their own service game but Nishikori did see two break point chances come and go in game five.
Leading 5-4, Berdych sensed an opportunity on the sturdy Nishikori serve but was denied the lead when a backhand slice ballooned over the tramlines. The Czech's caution would be his undoing as Nishikori wriggled away to level at 5-5, the first time a set in the tournament had been all square after 10 games.
The former Wimbledon finalist's first serve percentage dropped below 50% but he was able to swat away two break point chances. But when a third came the way of Nishikori he converted as Berdych found the net. The Japan number one then reeled off five straight games to take the opening set and a 2-0 lead the start of the second.
Berdych looked on the precipice but it was a situation that produced his best tennis as Nishikori's serve fell flat. It was the turn of the number six seed to dominate with five consecutive games of his own to square the match and force a third set for the first time in the tournament.
The tightness of the contest continued deep into the the third set with Nishikori missing two break chances in game two, but Berdych was otherwise consummate in his approach. However, the 25-year-old Japanese player would be the one to keep his nerve, breaking a jaded Berdych before a backhand down the line capped a fine match lasting over two hours.