ATP World Tour Finals | Murray wins a marathon against Nishikori

In what turned out to be a marathon encounter for the Briton’s second win in the tournament to hold off Novak Djokovic attempt to reclaim the top ranking, Murray had to dig deep into his reserves to overcome the gallant fifth-seeded Japanese, who appeared set to win his third meeting against Murray after clinching a pulsating opening set on tie-break.

However, Murray came back strongly to open up a 4-2 lead in the second set, but allowed Nishikori to level at 4-all. Murray subsequently broke Nishikori and then saved two break points before clinching the set on his third set point opportunity when the Japanese sent a backhand long.

The decider was edge-of-the-seat stuff. Although Murray broke his opponent in the third and fifth games, Nishikori had his chances and even won two games when the Brit was on the brink of victory at 5-2.

“I’m a bit tired, obviously,” Murray told a press conference. ”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 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,” he added.

US Open champion Wawrinka left the passive showing of the first outing against Nishikori in the back as he beat Cilic 7-6, 7-6 for his second win in the tournament to keep his semi-final hopes alive.

Wawrinka will now play Murray on Saturday with the Briton holding a 9-7 head-to-head record.