Serena Williams serves up Sony romp

KEY BISCAYNE, Fla. -- Unhappy about losing a point midway through the second set, Serena Williams stood near the backstop, gritted her teeth and swung her racket as hard as she could, as if trying to coax even more ferocity from her strokes.

That hardly seemed possible. Williams pummeled the ball plenty Monday, matching a career high with 20 aces and whacking enough thunderous groundstrokes to beat Samantha Stosur 7-5, 6-3 and advance to the quarterfinals of the Sony Ericsson Open.

"My serve was hot," Williams said. "I was like, 'That's pretty cool.'"

She avenged a loss to Stosur when they last met in the U.S. Open final in September.

"That wasn't in my mind," Williams said. "I just thought, 'This is a new game.'"

Older sister Venus won her third consecutive three-set match, hitting 13 aces as she outlasted No. 15-seeded Ana Ivanovic 6-7 (4), 6-2, 6-2. Williams is playing in her first tournament since withdrawing from the U.S. Open last August after being diagnosed with an autoimmune disease.

"I come out on court knowing I can play well, but almost with no expectations," Williams said.

Top-ranked Victoria Azarenka lost 10 of the first 11 games, then rallied to remain unbeaten this year by beating No. 16-seeded Dominika Cibulkova 1-6, 7-6 (7), 7-5. Azarenka was two points from defeat five times, but swept the last three games and extended her winning streak to 26 matches, all in 2012.

"I'm proud of the way I fought," she said. "With my game I don't think I'm really pleased, but it doesn't really matter. The most important is that I found the resources."

Also reaching the quarterfinals was No. 2 Maria Sharapova, who overcame 11 double-faults to beat Ekaterina Makarova 6-4, 7-6 (3). Sharapova won despite committing 52 unforced errors and losing her serve four times.

In other women's play, former No. 1 Caroline Wozniacki defeated No. 23 Yanina Wickmayer 7-6 (6), 6-0. Reigning French Open champion Li Na rallied past Sabine Lisicki 3-6, 6-4, 6-2, and No. 5 Agnieszka Radwanska defeated 18-year-old Garbine Muguruza Blanco 6-3, 6-2.

The No. 10-seeded Williams lost only six points on her first serve against the No. 6-seeded Stosur, but had to rally after being broken in the first game of each set.

Williams failed to convert her first seven break-point chances, then muscled her way back into the match. She also showed finesse, such as when she chipped a forehand drop shot that barely cleared the net for a dainty winner.

Is a shot like that fun?

"It was more nervous than fun," Williams said. "I was like, 'OK, is it going to go over?' Then it was, 'Now, oh, is she going to get it?' So it was more like that as opposed to fun."

Williams' best stroke was her serve. She hit six aces during a 20-point game to hold for 3-2 in the second set. After falling behind love-40 in the final game, she smacked three aces and eventually reached match point.

Her final serve spun so violently it kicked head-high to handcuff Stosur, who could only push the ball wide. A jubilant Williams hopped, skipped and pumped her fists.

Williams is playing in her first tournament since January after being sidelined by a left ankle injury. She hasn't won a title since August, and seeks a record sixth Key Biscayne championship.

"I'm really trying so hard," she told the crowd. "My mom gave me the ultimate pep talk last night, so thanks, Mom."

Her sister Venus was to face Ana Ivanovic in the last fourth-round match Monday night. Venus is playing in her first tournament since withdrawing from the U.S. Open last August after being diagnosed with a fatigue-causing autoimmune disease.

"We both have been through a lot," Serena said. "And each match, whether we're beating top-10 player or a top-80 player, we really thoroughly enjoy it and want to do really well."