MIAMI : Guillermo Canas stunned world No 1 Roger Federer for the second time in three weeks, earning a 7-6 (7/2), 2-6, 7-6 (7/5) win in the fourth round of the ATP/WTA Miami Masters Series event.

Canas's win Tuesday validated a convincing straight-sets upset on March 11 at the Indian Wells Masters Series tournament that snapped Federer's 41-match winning streak.

Canas improved to 3-1 all-time against the tournament's top seed.

Just hours earlier, Serena Williams humiliated the top-seeded Maria Sharapova for the second time this year with a convincing 6-1, 6-1 fourth round win at the US$6.9m tournament.

Williams' dismantling of Sharapova looked remarkably similar to her 6-1, 6-2 demolition in the Australian Open final and further confirmed her renewed commitment to tennis after over than a year of injuries and distractions.

"I know if I'm playing well, then anything can happen," said Williams, a two-time champion of this event.

Williams deployed her power game to neutralize the length and court coverage of the 6-1 Sharapova, whose grunts and groans intensify with the importance of the points and could easily be heard above the crowd.

As she was in Melbourne eight weeks ago, the 13th-seeded Williams was relentless, winning the last five games of the first set and the last six of the second set. She never faced a break point and converted five of her own.

"I never think about, 'I'm winning. It's easy.' Because every point, Maria is a fighter. She doesn't give up," Williams said.

Williams is looking less like the overweight, undermotivated player she was last year and more like the eight-time Grand Slam winner.

"I don't know anyone who's won eight Grand Slams and had so many doubters in her life," Williams said.

Tuesday's romp came a day after she was heckled during her third-round win over Czech Lucie Safarova.

Told by the heckler to "Hit the net like any Negro would," Williams was rattled at the time. "It was over once the match was over," Williams said.

Meanwhile, Sharapova failed to reach the quarter-finals as the top seed for the second straight event, raising questions about her game.

"You obviously go out on the practice court and work on it," she said. "It'll take time, but I'm sure I'll get there."

Canas also has had a long road back. In September, he returned from a 15-month suspension for using a banned substance and has been playing his way back into form.

Canas immediately put the pressure on the two-time defending champion by winning the first set.

Federer found his form in the second set but continually struggled with his return game that saw him convert just four-of-16 break points.

Federer's second straight early departure again opens the door for second seed Rafael Nadal of Spain, who takes on Juan Martin Del Potro of Argentina. Nadal won the Pacific Life Open, his first tourney victory since the 2006 French Open.

Third-seeded Andy Roddick continued his strong play this season with a 7-5, 6-3 victory over 13th-seeded David Ferrer of Spain.

Up next for Roddick is 12th seed Andy Murray of Britain, who stormed back from the brink of elimination for a 2-6, 7-5, 6-3 victory over Paul-Henri Mathieu of France.

"There was somebody in the crowd who at 5-3, match point down, shouted at me, 'Murray, you've got nothing,'" Murray said. "And I was like, 'Well, I do.'"

- AFP/yy