By Martyn Herman
LONDON (Reuters) - Andy Murray had to trawl deep into the bottom of his energy reserves to outlast Japan's Kei Nishikori 6-7(9) 6-4 6-4 in a monumental battle lasting more than three hours at the ATP World Tour Finals on Wednesday.
The new world number one looked in trouble when Nishikori edged an epic tiebreak to claim the opening set in 85 minutes, but hit back to avenge his quarter-final loss at the U.S. Open, his last Tour level defeat before his astonishing 21-match winning streak.
Nishikori recovered from an early let-down in the second set and looked close to ending the Scot's remarkable streak when he broke back for 4-4 and had a point for a 5-4 lead.
Despite looking weary Murray broke again before levelling the match by holding his serve after saving two break points.
Even when Murray stormed 5-2 ahead in the decider there was still a twist as Nishikori mounted a final desperate assault, breaking Murray on a double-fault, but the Scot sealed victory at the second time of asking after three hours 20 minutes.
With two victories already in the bag in John McEnroe group, Murray will qualify for the semi-finals with a match to spare if Marin Cilic beats Stan Wawrinka in the evening session.
With Novak Djokovic, his rival to end the year as number one, already in the semi-finals, Murray could well have to win the Tour Finals for the first time if he is to keep hold of the top spot he took from Djokovic last week.
(Reporting by Martyn Herman, editing by Pritha Sarkar)