Both top seeds at the Sony Ericsson Open in Miami, Florida have lost in rematches against players who recently won similar upsets.
Guillermo Canas of Argentina beat world No. 1 and top seed Roger Federer of Switzerland for the second time this month, 7-6, 2-6, 7-6. Two weeks ago, Canas ended Federer's 41-match winning streak at Indian Wells. The Argentine repeatedly chased down shots and forced the two-time defending champion into 51 unforced errors.
Also Tuesday, Australian Open tennis champion Serena Williams of the United States easily defeated top-seeded Maria Sharapova of Russia. The 13th-seeded Williams overpowered Sharapova, 6-1, 6-1, in a rematch of their Australian Open final earlier this year. Williams next faces No. 8 Nicole Vaidisova of the Czech Republic for a berth in the last eight.
Meanwhile, ninth-seeded Russian Anna Chakvetadze advanced to the semifinals, battling from behind to beat No. 15 Li Na of China, 4-6, 7-5, 6-2.
In men's play, 12th-seeded Andy Murray of Britain fought off two match points and rallied for a 2-6, 7-5, 6-3 win over Frenchman Paul-Henri Mathieu. In the quarterfinals he will play third-seeded American Andy Roddick, a 7-5, 6-3 winner over and Spaniard David Ferrer.
Tommy Robredo of Spain, seeded sixth, ousted Czech Radek Stepanek, 7-6, 5-7, 7-6. Juan Ignacio Chela of Argentina defeated American qualifier Amer Delic, 6-3, 6-2.