Federer, who has failed to win any of his last four tournaments for the first time since becoming world number one more than three years ago, mistimed the ball more than usual and had to save five points to avoid going a break of serve down in the final set during an unconvincing 6-3, 2-6, 6-4 second round victory.

True, the world number 48 from Argentina has a good clay court record this year, and conditions were difficult, but Federer will need to play better to convince many people that he can prevent Rafael Nadal from winning this title for the first time on Sunday.

The match was played in very cool temperatures - only 11 degrees Centigrade - and with rain beating fiercely on the centre court roof during various stages of the match the atmosphere became very damp and the balls uncomfortably heavy.

"I had to fight to win and it was definitely a hard fought victory," said Federer. "The conditions were difficult but my opponent was good as well.

"Things were not always looking good today and I came out of a few difficult situations. It was not all straightforward.

"It was important to stay focused and hope for the best in the third set and hope to come through."

There were signs that Federer might not be able to win as routinely as expected as early as the second game, when he failed to hang on to a break of serve and needed to break again in the eighth game before he could capture the first set.