WIMBLEDON, England -- Jennifer Capriati, playing well below her best, defeated Russian Tatiana Panova 6-4, 6-4 to reach the last 16 at Wimbledon and stay on course for the Grand Slam of major titles on Friday.

Fifth seed Serena Williams joined her in the fourth round by blasting her way past Switzerland's Emmanuelle Gagliardi 6-1, 6-2.

Capriati came back from 4-1 down, after two breaks of serve, in the second set as Panova's game resistance to the American fourth seed's power suddenly crumbled.

Panova, seeded 32, caused the Australian and French Open champion major problems with her accuracy and length of shot, especially on her two-handed backhand, and she broke Capriati's serve in the first game of the match.

Capriati, 25, emerged from a flurry of breaks to take the set in 39 minutes on Centre Court and, after coming through a service game with eight deuces at 4-2, she pulled away to win.

"I agree I had lapses of concentration," Capriati said. "In the beginning everything was kind of off.

"Overall it was just a hard match to play," she said. "But I turned it up at the end. I was happy the way I finished it."

She plays Sandrine Testud, seeded 15, after the Frenchwoman beat Ai Sugiyama of Japan 6-7 6-2 6-2.

"You have to mentally prepare yourself for these kind of days. Hopefully it will get tougher and tougher the next rounds," Capriati said.

"I don't take any opponent lightly but, from here on in, I certainly can't do that."

The only game the 96th-ranked Gagliardi won in the 20-minute first set was on a break in the third when Williams, a semifinalist here last year, gave away every point with unforced errors.

After going a break up early in the second set Williams again gave away her first game. But the American broke straight back to love and won the next three games for victory.

"I didn't think I played very well at all today. I couldn't get my feet moving and made a lot of unforced errors," Williams said. She plays Magdelena Maleeva, seeded 12th, in the fourth round after she beat American Amy Frazier 6-3 6-2.

In other action, promising Russian teenager Lina Krasnoroutskaya thundered into the last 16 with a 6-3, 6-4 victory against Austrian qualifier Barbara Schwartz.

Spain's Conchita Martinez, champion in 1994, beat Lilia Osterloh of the U.S. 6-2, 6-3 after the first matches on court were interrupted for about 90 minutes by rain.

Tenth seed Elena Dementieva of Russia was thrashed 6-0, 6-2 by Germany's Anke Huber with the first set whistling by in 12 minutes.