Andy Murray had to fight back from behind to win another excellent match against Kei Nishikori in the ATP World Tour Finals, putting the world number one on the brink of the semi-finals.
The pair had already played out an epic five-set match in the Davis Cup in Birmingham in March, that Murray won, while Nishikori secured a superb win over the Briton in the US open quarter-finals.
Bidding to overtake Stan Wawrinka as world number three, Nishikori took the first set on a tie-break as Murray struggled to find the brilliant form so often on display in recent weeks.
However, Murray dug deep and relied on the determination and endurance that has made him so hard to beat in the last few months, taking both the second and third sets 6-4. The match lasted for 320 minutes, the longest three-set match in the history of the tournament.
It means Murray has now won 21 matches in succession, and needs one more win to be sure of qualification.
He will play Wawrinka in the final match of the round-robin stage knowing he is through unless he were to suffer a straight-sets defeat to the Swiss combined with Nishikori beating Marin Cilic in the other match.
Indeed, Murray would already be in the last four had not Wawrinka defeated Cilic 7-6, 7-6 in the second match, with the Swiss star bouncing back from his opening match defeat to Nishikori with a display that suggested he had from the fitness problems that had plagued his performance against the Japanese number one.
Commenting after his victory, Murray reflected on the implications as he seeks to retain his world number one ranking ahead of Novak Djokovic: "It’s obviously important to win matches to give yourself the best chance to go through. 200 points for each match here is quite a lot, as well. Obviously that increases as you get into the semis, potentially in the final. It could come down to a match between me and Novak.
"Who knows what's going to happen [over] the next few days? Just from my side, [I need to] concentrate on trying to win my own matches, get through as many as I can, make it as tough as possible for Novak to jump me."
The pair may yet meet in the semi-finals or final, with Djokovic making it three wins from three today by thrashing David Goffin 6-1, 6-2 in his final match. Goffin was making a single appearance as a substitute for the injured Gael Monfils, who was already out after two losses.
Fans booking corporate hospitality for The Championships, Wimbledon next summer could be witness to dramatic developments in the ongoing rivalry between the pair, not least if they meet again in the final as they did in 2013.
Because Murray is the reigning champion, he would need to retain the title to keep his ranking points, whereas Djokovic's early exit this year means he has an opportunity to boost his tally. However, before then the Serb has to try to defend the Australian and French Open titles, with Murray hoping to go one better than last year after losing both finals.