Andy Murray all but assured of his place in the semi-finals of the ATP World Tour Finals in London with a grueling 6-7(9), 6-4, 6-4 victory over Kei Nishikori in what was recorded as the longest match in Tour Finals history. 

The Scot will face Stan Wawrinka in the concluding round robin encounter and could face Novak Djokovic in a straight shootout for the world number one berth in the final on Sunday with the Serb in commanding control of Group Ivan Lendl

Tight opening set

Murray entered this afternoon's meeting boasting a 7-2 record against his Japanese counterpart but ought to have been conscious of the pain Nishikori inflicted upon him at the U.S. Open during the summer, prevailing in an energy-sapping five-set quarterfinal. Murray, though, could take solace from his positive record over the world number five this year.

The opening set stayed on serve until the third game when the Japanese fashioned the first break point of the afternoon. The pair traded no less than 17 breaks of serve during their memorable encounter in New York in September but Murray clung on to prevent an early struggle, Nishikori netting a promising forehand.

The world number five, nominally lethal on the forehand wing, was racking up the unforced errors but was able to manufacture another two break points just two games later. Murray's serve had wobbled to begin the match, frequently failing to break the 75mph mark with his second serve, but saved both with a pair of commanding first serves down the T.

The intensity lulled until 5-5, with Nishikori netting a backhand down the line to squander yet another break point. The Scot was curiously fist pumping despite being on the losing end of rallies. A tie-break awaited.

The pair traded mini-breaks and parity was restored as the both players headed for the benches at 3-3. Murray's level dipped drastically and the world number one afforded his opponent with two mini-breaks and, an ace later, three set points. Nishikori, however, squandered all three and was nonplussed and how he wasn't able to close out the set with his third.

In seeming command of the rally, the Japanese rushed to the net and swept a forceful volley to Murray's backhand side. Glued behind the baseline, the indefatigable Brit scurried over and executed the most mesmeric backhand passing shot we've likely seen this year.

However, Murray's efforts were in vain when he sent a forehand wide at 9-10 in the tie-break and Nishikori closed out the first set.

Murray was forced to stretch every sinew to overcome the Japanese number one (Photo: Clive Brunskill/Getty Images Europe)

Murray resumes control

Riding the crest of his first set endeavors, Nishikori quickly surrendered his opening service game thanks to a net cord and Murray, with his first serve percentage on the rise, raced away into a commanding advantage.

The Japanese was afford a brief window of opportunity on Murray's serve at 4-3 and converted with an arrowed backhand crosscourt.

Determined to correct his errors in the previous game, Murray was handed a break point opportunity when Nishikori's drop shot proved too inviting. Stretched to the limit, Nishikori netted a backhand crosscourt and Murray would serve out the set to tie the match one apiece.

After nearly two and a half hours on court, and the possibility of Murray playing another three matches before the tournament concludes, the Scot reasserted his superiority in the deciding set quickly.

Nishikori was left to rue a pair of agonizing net chords as the world number one broke for a 2-1 lead and, aided by a double-fault at 30-40 in the fifth game, consolidated his advantage for 4-1.

Murray was presented with the opportunity to close out the match at 5-2 but failed to do so, hawkeye adjudging a forehand to have drifted wide. 

Nishikori offered brief resistance but Murray closed out the victory.