Roger Federer is in danger of losing his spot as the tennis world's number one after an opening-match defeat in the Toronto Masters.

The Swiss star was defeated 2-6, 7-5, 6-4 by world number 22 Gilles Simon in his first match since losing the Wimbledon final to Rafael Nadal.

And with Nadal moving past American Jesse Levine in a 6-4, 6-2 victory, Federer's lead at the top of the world rankings could be in jeopardy.

"It's important to stay positive", said the 26-year-old. "The hardcourt season has just started and we have nine months of it.

"It's not the end of the world, but I wish I could have started better. I like this event and I've done well here," the two-time Toronto winner added.

Federer raced to a 4-1 lead on his way to taking the first set only for his French opponent to rally in rainy conditions for his "best victory".

"I don't think that you win so many times against the number one in the world," Simon was quoted by the Associated Press news agency as saying.

"It happens maybe in the career of a player maybe two, three times if you are lucky."

Federer added: "I've got to regroup and look forward to the Olympics and the US Open. This is really where I want to win. I have to make sure that I'm ready to."
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