Canas now holds a 2-1 career record against Federer

The world number one, who has won the tournament for three years in a row, was previously unbeaten since August.

He looked sluggish throughout but refused to blame the pressure of the unbeaten run for his performance.

"It just shows you how tough it is. It was just a grind for me from the start. It had to happen so it's OK," he said.

Interview: Roger Federer

Before the game, the last player to have beaten Federer was Andy Murray in Cincinnati last year, and the Swiss had been closing in on Guillermo Vilas's 46-match record streak.

"You think it's pressure? It's no pressure at all because I take it match by match," Federer added.

It's great to beat the number one, I feel perfect Guillermo Canas

"I'm concerned about winning my first-round match against a lucky loser. I was struggling but it was tough.

"The first match is always difficult, but I've had an incredible run, not losing an opening game for, I think, over two years.

"So I'm really happy about that. Sooner or later it had to happen, so it's OK. It's no problem."

606: DEBATE Canas is having a great year since his suspension so I'm not too surprised ZS

Canas, the former world number eight, only returned to the tour last September after a 15-month suspension for doping offences, and was understandably delighted at his result.

"It's great to beat the number one, I feel perfect," said the 29-year-old. "I dream about this, but I didn't expect."

Generally, it was not a good day for the big names and tournament seeds.

Lleyton Hewitt, Marat Safin, Tomas Berdych, Tommy Robredo and Radek Stepanek all made second-round exits, at the hands of Janko Tipsarevic, Nicolas Mahut, Michael Russell, Gilles Simon and Carlos Moya respectively.

Argentine 10th seed David Nalbandian made a poor start against German Phillip Kohlschreiber before recovering to win the 1-6 7-5 7-6 (7-1).

Croatian eighth seed Ivan Ljubicic was also given a scare as he dropped the first set against Colombia's Alejandro Falla before going on to win 6-7 (4-7) 6-4 6-4.