Former French Open champion Stan Wawrinka posted another solid performance on Thursday.

Yet to drop a set at the tournament so far, the three-time Grand Slam champion played aggressively and close to the lines throughout, hitting 45 winners to beat Alexandr Dolgopolov 6-4, 7-6 (5), 7-5.

"The most important thing for me is the way I play," said Wawrinka, who beat Novak Djokovic in the final two years ago. "It was a difficult challenge because he is varying and mixing his shots well."

Dolgopolov made only 18 unforced errors but Wawrinka played a flawless baseline game, punctuated by some superb shots.

"It was a very, very good match," said Wawrinka, who will next take on Italian Fabio Fognini.

"Again a tough match," Wawrinka said. "Kind of player like Dolgopolov, unpredictable."

Earlier, Karen Khachanov advanced to the third round of a Grand Slam tournament for the first time by upsetting 13th-seeded Tomas Berdych 7-5, 6-4, 6-4. The 21-year-old Russian had 12 aces against Berdych and set up a big server contest. He will take on No. 21 seed John Isner for a spot in the fourth round. The American player hit 21 aces in his 6-3, 7-6 (3), 7-6 (2) victory over Paolo Lorenzi.

In the women's draw, Agnieszka Radwanska won back-to-back matches for the first time since reaching the final in Sydney in January.

Radwanska, seeded ninth at the French Open, beat qualifier Alison Van Uytvanck 6-7 (3), 6-2, 6-3.

Earlier in the clay-court season, Radwanska has missed the Madrid and Rome tournaments because of a right foot injury.

"I have been struggling with my health for a couple of weeks," Radwanska said. "I only had a week practice, so I am just very happy to be in the third round."

Among the women also advancing to the third round were No. 5 seed Elina Svitolina and No. 14 Elena Vesnina.