Serena Williams loses to Wozniacki at Key Biscayne

Serena Williams' bid for a record sixth Key Biscayne title ended on Tuesday  when she lost in the quarterfinals of the Sony Ericsson Open to former No. 1 Caroline Wozniacki, 6-4, 6-4.

"I made her run," Wozniacki said.

Wozniacki served well and was content to keep the ball in play from the baseline, using her retrieving skills to extend rallies until Williams would make a mistake. Williams hit 34 winners to 12 for Wozniacki, but also committed 36 unforced errors to the Dane's 13.

"Everyone I play always plays the match of the year," Williams said.

Williams, seeded 10th, was playing in her first tournament since January after being sidelined by a left ankle injury. She hasn't won a title since August.

"I probably played about 20 percent," Williams said. "I just made a tremendous amount of errors. There's no reason for that. I'm older and I shouldn't do that. There's no excuse. I've just got to stop that. It's silly."

Rafael Nadal swept five consecutive games midway through his match, propelling him to a 6-4, 6-4 win over Kei Nishikori to reach the quarterfinals.

The victory was by far Nadal's most taxing of the tournament, and he took a medical timeout late in the opening set for treatment of his troublesome left knee. Even so, he's one round closer to his first Key Biscayne title.

"I am not probably in perfect condition today with the left knee," he said. "But the important thing is to try to win as many matches as possible. For me this is an important tournament, and every victory has very, very big value for me, especially without being perfect."

Nadal, a three-time runner-up at Key Biscayne, lost the final last year to Novak Djokovic, and they could meet again Sunday. The top-ranked Djokovic reached the final eight by beating No. 17-seeded Richard Gasquet 7-5, 6-3.

No. 2 Maria Sharapova became the first semifinalist when she drubbed reigning French Open champion Li Na 6-3