Andy Murray overcame a gutsy Kei Nishikori to record a three-set victory at the ATP World Tours Finals in London.
Murray, who lost his last meeting against Nishikori in the US Open quarter-finals this year, breezed past Croatia's Marin Cilic in his opening group match but Wednesday's contest was a lot more difficult.
The world number one traded blows with his Japanese opponent in the first set and, with no breaks of serve in the first 12 games, the pair were forced to play out a tie-break.
It was the 26-year-old from Matsue that managed to take the marathon tie-break 11-9 and move to within a set of wrapping up a second straight win, having already beaten Swiss Stanislas Wawrinka.
The second set was another war of attrition, with the duo going toe-to-toe, but it was Murray, the reigning Wimbledon and Olympic champion, who was able to produce the goods.
Great Britain's 2015 Davis Cup hero won the set 6-4 to force a decider and he used the momentum to his benefit, as the gruelling match started to take its toll on the Japan ace.
The three-time Grand Slam champion produced some brilliant shots to take control of the contest and he raced into a 5-1 lead.
However, Nishikori wouldn't go down without a fight and he took the next three games to make it 5-4.
But Murray, who came into the event on the back of four straight tournaments wins, dug deep to the delight of the fans and served out the match, winning 6-4.
The Glaswegian is now on the brink of reaching the semi-final stage for the first time which will happen if Cilic defeats Wawrinka in the evening session.