London : He may have been crowned the world champion for the fifth time last week, but Swiss superstar Roger Federer knows that the gap between him and the rest of the players is getting narrower by the day.

"That he [Juan Martin del Potro] got so close with the other two guys [Andy Murray and Fernando Verdasco] is quite incredible. I am, in a way, surprised myself that it finally came down to a couple of games," Federer told media late on Friday after squeaking through to the semifinals at the Barclays ATP World Tour Finals.

Awaiting result

The O2 Arena was abuzz on Thursday night with spectators staying put to see who the two semifinalists from Group A would be after del Potro had beaten the world champion in three sets. Del Potro stayed on court and invited good friend and Manchester City striker Carlos Tevez to hit around with him till the ATP officials worked out who was through to the last four stages of this year-end final.

It eventually came down to one game after all three had identical 2-1 win/loss records: Murray had won just one game fewer than the Argentinian.

The format for this year-ending tournament is such that even someone like Federer who had a 2-0 record going into his final round match against Del Potro could have been dumped out of a place in the semifinals, had he lost in straight sets to his Argentinean opponent.

After being crowned the world champion for the fifth time, Federer became just the second player in the history to regain the year-end No 1 ranking. "The only thing that was important to me was the set I needed to win, trying to win the match. The rest you block out and you concentrate on the match because I don't want to lose against fellow rivals," Federer stated.