Roger Federer's 41-match winning streak came to a sudden halt while Lleyton Hewitt claimed a bad back was his undoing at the Masters Series event in California.

World No.1 Federer suffered a stunning 7-5 6-2 upset defeat by Argentine Guillermo Canas while Hewitt was ousted 7-6 (7-3) 4-6 6-2 by Serb Janko Tipsarevic in second round matches.

Ten-time grand slam champion Federer had been hoping to break the professional era record of 46 successive wins set by Argentine Guillermo Vilas with a tournament win.

But he was left with a tally of 41 when Canas - who lost in qualifying only to be granted a lucky loser's spot in the main draw when Belgian Xavier Malisse withdrew - rolled him in straight sets.

Federer said the pressure of closing on another record had not contributed to his defeat.

"It's no pressure at all because I take it match by match," Federer said.

"I'm concerned about winning my first round match against a lucky loser.

"It just shows you how tough it is. Today was just a grind for me from the start. First-round match is always difficult, but I've had an incredible run, not losing in the first round for over two years. So I'm really happy about that. Sooner or later it had to happen, so it's OK."

Federer celebrated his 161st consecutive week as world No.1 last month, breaking the 30-year-old record of American Jimmy Connors.

But it counted for little as Canas outplayed him consistently from the baseline, sealing victory with a powerful inside out forehand.

The Argentine, who achieved his career-high ranking of world No.8 in 2005, returned to the tour last September after serving a 15-month suspension for a doping offence.

He became the first lucky loser to beat a world No.1 since Australian Sandon Stolle stopped Thomas Muster in the first round of an ATP Dubai tournament 11 years ago.

"It's great to beat the number one, I feel perfect," the 29-year-old said.

"I dream about this, but I didn't expect it. I have confidence in my game but I know it's going to be tough."

Meanwhile former world No.1 Hewitt, who won the title in Las Vegas last week, appeared to injure his back in the first game against Tipsarevic and had trouble moving for the rest of the match.

"It didn't get any better the whole time," Hewitt said.

"I knew something wasn't right. It affected me on movement and return of serve. I had to adjust my whole position.

"I'm a little concerned. It's frustrating because I've been timing the ball well."

Hewitt was watched by his former coach Darren Cahill, but the former US Open and Wimbledon champion played down reports they might work together again.

"I have no idea," Hewitt said. "I still have to work things out and see where I want to go and see who the best person is to take me there.

"Darren is doing TV commentary here this week and he came a couple days early to work with Davis Cup guys like me and Guccione and I was the only guy left so he was watching me."

Briton Andy Murray, the last man to beat Federer back in August, reached the third round here along with Australian Open runner-up Fernando Gonzalez, eighth seed Ivan Ljubicic and David Nalbandian.

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