Switzerland's Roger Federer reacts in a point against Argentina's Juan Martin del Potro during their ATP World Tour Finals tennis match at the 02 Arena in London, Thursday, Nov. 26, 2009. (AP Photo)

LONDON (Reuters) – World number one Roger Federer squeezed into the semifinals 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 organizers 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 semifinals 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 semifinals by virtue of a better game percentage.

Despite an off-color 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 favorite 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 told reporters. “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.”