Unlucky break for world number four Andy Murray [GALLO/GETTY]
A one game margin knocked Scotland's Andy Murray out of a semi-final spot at the ATP World Tour Finals in London, despite winning two matches in the round-robin phase of the season-ending event.

Murray beat Fernando Verdasco but was still eliminated because US Open champion Juan Martin del Potro managed to defeat Roger Federer in the late match.

All three of those players completed the round robin with identical 2-1 records in Group A, but Murray was on the short end of a complicated tiebreaker that came down to a total game-winning percentage.

"It goes down to the percentage of games,'' said Murray, who won all three round robin matches last year but lost to Nikolay Davydenko in the semi-finals.

"The people that go through are the ones that deserve to.''

One game

Murray's 6-4 6-7 7-6 victory over Spain's Fernando Verdasco meant any win for Federer later would have sent the Scot through but Federer suffered badly again at the hands of the south American who beat him in the US Open final in September.

Del Potro beat the Swiss champion 6-2, 6-7 (5), 6-3 victory - sending Murray home for the offseason.

Despite an off-colour performance against Del Potro in which he came within a whisker of elimination himself, Federer topped the group with a 44-40 games record.

A bemused-looking Del Potro edged home favourite Murray by one game having finished 45-43 compared to Murray's 44-43 although he seemed unaware of his fate after sealing victory in an entertaining scrap lasting just over two hours.

"Sure, it's confusing," Federer said.

"It's hard for Murray. I mean, I asked Juan Martin myself at the net, 'Did you make it or not?' He said, 'I don't think so.'

"So that's the story I got. Of course, you got to feel sorry for the guy who didn't make it."

A straight sets defeat for Federer would have knocked out the 15-times grand slam champion and when Del Potro had a 5-4 lead in the second set tiebreak with two serves to come it looked bleak for the Swiss maestro but a miss-hit return caught Del Potro off guard and pounced to take it into a decider.

Juan Martin Del Potro waits for news about his progress [GALLO/GETTY]
Lucky Swiss

"I knew I couldn't lose in two sets because I knew that was going to knock me out," said Federer.

"That's why I was very excited having won the second set.

While Federer was effectively through by taking the second set, the sums meant 21-year-old Del Potro, faced with needing to win the final set 6-3 or better and despite some nervous moments, managed to kill off Murray's hopes.

"It was very strange," he Del Potro.

"I'm happy to be in the semi-finals, but it's strange. I took my opportunities and that's what you need to do against the best player in the world."

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.

"That he got so close with the other two guys, it's quite incredible,'' Federer said of Murray.

"I am, how do you say, in a way surprised myself it came down to a couple games.''

Source: Agencies