Andy Murray faces an anxious few hours to see if he has sealed a place in the semi-finals of the ATP World Tour Finals after overcoming Fernando Verdasco 6-4 6-7 7-6 in his final round-robin match.

Murray would have secured a spot in the last four if he had tamed Verdasco in straight sets but must now await the result of Thursday's second match between world number one Roger Federer and U.S. Open champion Juan Martín del Potro.

If the Swiss topples the towering Argentine, Murray will extend his stay at the O2 Arena but if Del Potro wins the evening showdown, calculators will be needed to work out which two players progress to the semis from Group A.

Murray, seeking a seventh title of the season, was fortunate to gain his only break in the first set when Verdasco slapped an easy volley into the net to the surprise of the 17,500 fans.

The Spaniard then gatecrashed the British party by stealing the second set 7-4 in the tiebreak, thanks to a double fault from the misfiring Murray.

Verdasco fought valiantly in the third set but, as the clock hit the three-hour mark, he hit a tired forehand into the tramlines to hand Murray the tiebreak 7-3 and a victory that brought an almighty roar of relief from the home crowd.