KEY BISCAYNE, Fla. — Volleys came at Serena Williams in a flurry. She sprinted to her right to chase one down, then to her left, then right, then left, finally ripping a backhand winner to end the frantic exchange.

Williams always seems to rise to the challenge at the Sony Ericsson Open, where she has won four titles and is back in the quarterfinals. She beat Kaia Kanepi 6-3, 6-3 today and will next play top-ranked Justine Henin, renewing one of the best rivalries in tennis.

The No. 8-seeded Williams looked sloppy in a third-round victory, committing 60 unforced errors, but she pared that total to 24 against Kanepi. It was clear Williams meant business: She screamed "C'mon!" when she hit an ace, then shrieked when she hit a sloppy shot, and both times she could be heard in the top row of the stadium.

"I definitely feel like I was focused," Williams said. "I felt like I had to be. The other match was definitely a good eye opener."

She's sure to be fired up again tomorrow when she faces Henin. Williams has lost their past three meetings, all last year, at the French Open, Wimbledon and the U.S. Open.

"We definitely bring out some of the best tennis in each other," Williams said. "And she tends to play really well against me — probably better against me than other opponents. So it's definitely a good match for me."

It's a rematch of last year's Key Biscayne final, which Henin lost after Williams erased two championship points.

"Actually it's a very good memory from last year, even if I had match points and I lost the match," Henin said. "It was a day that I understood that could win against Serena, and that I could do it in Grand Slams three times in the same year."

Tomorrow's winner could meet Venus Williams in the semifinals. Three-time champion Venus, seeded sixth, advanced by beating 17-year-old Caroline Wozniacki 6-3, 6-3. Henin defeated Elena Vesnina 6-2, 6-2.

No. 1 Roger Federer and newly engaged Andy Roddick reached the fourth round on the men's side. But Lindsay Davenport hit a bump in her career comeback when she lost to Dinara Safina 6-3, 6-4.