MONTPELLIER, France -- Top-seeded David Goffin of Belgium reached the quarterfinals of the Open Sud de France on Wednesday by beating French veteran Gilles Simon 6-4, 6-2.

The 33-year-old Simon had won two of their three previous matches but dropped his serve six times. Goffin next plays Ricardas Berankis of Lithuania or Karen Khachanov, who played their second-round match on Thursday.

Sixth-seeded Russian Andrey Rublev joined Goffin in the last eight with a 6-2, 6-1 win against Frenchman Jeremy Chardy. He will face the winner of an all-French match between third-seeded Jo-Wilfried Tsonga and Nicolas Mahut.

In remaining first-round play, fifth-seeded Richard Gasquet of France swept aside Daniil Medvedev of Russia 6-0, 6-3. Gasquet did not face a break point and next plays Pierre-Hugues Herbert, who won 7-6 (4), 6-7 (5), 6-4 against Kenny De Schepper in an all-French match.

John Millman of Australia upset eighth-seeded Yuichi Sugita of Japan 5-7, 6-3, 6-4. Mahut trailed 7-6 (2), 5-2 against Dustin Brown when the German player retired with back pains. He went down clutching his lower back following a rally and pulled out shortly after receiving treatment when slumped on court.

"It's the first time I've experienced an end to the match like this. Dustin was completely dominating me in the second (set)," Mahut said. "When you see him in tears you can't celebrate such a win. Dustin's a great guy as well, everyone likes him."

Ruben Bemelmans of Belgium took only 50 minutes to beat French wild-card entry Calvin Hemery 6-1, 6-2.