Confusion reigns as Del Potro joins Federer in semis

World No 1 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 Briton Andy Murray literally missed out by a fraction.

The final round-robin action in Group A had players, tournament organisers and journalists scratching their heads as all three contenders ended with virtually identical records.

Del Potro summed up the confusion, admitting later that he did not even know he had joined Federer in the semi-finals until 25 minutes after their match had ended while Murray posted a Twitter entry simply asking 'Anyone know what's going on?'.

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 giant south American who beat him in the US Open final in September.

Federer, Del Potro and Murray all posted two wins and a 5-4 sets win/loss ratio meaning that calculators were as useful as tennis rackets to work out which two players would progress to Saturday's semi-finals by virtue of a better game percentage.

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 tie-break 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.

"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. The only thing that was important to me was the set I needed to win. That it got so close with the other two guys, it's quite incredible."

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," said. "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.

"When he served at 5-1 down against me in that set, maybe he had it on his racket, if he had held that game maybe he would have gone through," Federer said.