Federer, Sharapova suffer Miami upsets

The Sony Ericsson Open lost its two top seeds in contrasting upsets when Roger Federer and Maria Sharapova were bundled out in the fourth round of the Masters Series event on Tuesday.

Federer, twice winner in Miami, will get an early start to his claycourt preparations following a shock 7-6 2-6 7-6 defeat by Guillermo Canas.

It was the second successive tournament the energetic Argentine has beaten the world number one after snapping Federer's 41-match winning streak two weeks ago.

"I was really expecting to win, it was one of those matches I shouldn't have lost," Federer said.

Back on the ATP Tour after serving a 15-month doping ban, Canas battled Federer for two hours 38 minutes in a tight duel.

In sharp contrast to that marathon, Serena Williams needed just 58 minutes to humble Sharapova 6-1 6-1, avenging her sister Venus's loss to the lanky Russian in the third round.

Sharapova's exit left second seed and world number one Justine Henin as the remaining top player on the women's side after the Belgian secured a 7-6 7-6 win over Nadia Petrova sealed when the Russian's challenge on match point was ruled out.

Second seed Rafael Nadal of Spain and third seeded American Andy Roddick made smooth progress into the final eight.

Nadal swept past Argentine Juan Martin Del Porto 6-0 6-4 and Roddick advanced with a 7-5 6-3 win over Spain's David Ferrer.