LONDON: World number one Roger Federer squeezed into the semi-finals of the ATP World Tour Finals on Thursday despite a 6-2 6-7 6-3 defeat by Juan Martin del Potro but Britain's Andy Murray literally missed out by a fraction.

Argentina's Juan Martin Del Potro celebrates winning a game against Switzerland's Roger Federer during their ATP World Tour Finals tennis match at the 02 Arena in London November 26, 2009.[Agencies]

Switzerland's Roger Federer reacts after missing a shot against Argentina's Juan Martin Del Potro during their ATP World Tour Finals tennis match at the 02 Arena in London November 26, 2009.[Agencies]

The final night of round-robin action in Group A turned into a fraught night for the players and the tournament referee as all three players ended up with virtually identical records.

Murray's 6-4 6-7 7-6 victory over Spain's Fernando Verdasco meant victory for Federer in the evening session would have sent Murray through but the Swiss suffered again at the hands of the giant south American who snatched second spot in the group by virtue of a better game's percentage than the Scot.

All three players finished with two victories and with identical 5-4 sets records, meaning calculators were as useful as tennis rackets inside the O2 Arena.

However, Del Potro faltered and Federer pounced to take the match into a decider. With the group situation seemingly changing after every game, neither player seemed aware of what the sums meant: Del Potro was effectively faced with needing to win the final three games from 3-3 to stay alive.

Del Potro saved two break points, one with a ferocious forehand after a Federer forehand popped up invitingly off the net, and another with a huge second serve, to edge ahead 4-3.

Federer then imploded in the following game, serving two double faults and spraying a forehand wide at 15-40 to leave Del Potro with the task of holding serve to earn a memorable victory and leave Murray out in the cold.

After being clawed back to 30-30, the Argentine showed nerves of steel, sealing victory with a second serve ace.

It was tough on Murray who did precious little wrong in the tournament, although losing the third set of his second group match against Federer 6-1 ultimately proved costly when the equations were worked out on Thursday.

World number four Murray would have secured his place in the semi-finals and spared himself an agonizing night watching the TV if he had tamed Verdasco in straight sets.

Murray was fortunate to gain the only break of the contest at 4-4 in the first set when Verdasco hit the tape with an easy volley.

Verdasco levelled the match when he stole the second set tiebreak with the aid of a Murray double fault.

There was hardly a cigarette paper between the players in the deciding set but as the clock struck the three-hour mark a tired-looking Verdasco hit a forehand into the tramlines to hand Murray the victory. Sadly for the Briton, and the majority of the 17,500 fans in the arena, it was to prove in vain.

Verdasco's defeat ended a miserable outing for Spain at the tournament. The country was the only nation to field two representatives in the elite eight-man line-up but both Verdasco and Nadal, who was in Group B, are both eliminated.