Saint Petersburg - Three-time Grand Slam champion Stan Wawrinka advanced to the quarter-finals of the St Petersburg Open on Wednesday with a win over Russian fourth seed Karen Khachanov in two tie-break sets.

The 33-year-old Swiss star Wawrinka, a wildcard entry, knocked off world number 24 Khachanov 7-6 (12/10), 7-6 (7/1) and awaits the winner between defending champion Damir Dzumhur and Guido Pella.

"I'm really happy as the level of my play was really good today," Wawrinka said. "We both played really well, really aggressive.

"I was expecting a tough match and it was really tough. My level was great and I'm really happy with everything that took place on the court today."

Wawrinka, the former world number three, who is now down at 88 after a battle with injury, started confidently breaking his rival's serve early.

But the Swiss, who has been struggling to find his best form since returning to the ATP Tour after two operations on his left knee a year ago, suddenly lost his nerve to allow the local favourite to break twice in succession.

Khachanov, 22, was serving for the set but Wawrinka broke again to level and force a tie-break, closing it out at the sixth attempt having also saved two set points.

Wawrinka then raced through another tie-break to seal victory over Khachanov in the first meeting between the pair.

Fifth-seeded Spaniard Roberto Bautista Agut and Canada's Denis Shapovalov, the seventh seed, reached round two with respective wins over qualifiers Luca Vanni, 7-5, 6-2, and Adrian Menendez-Maceiras, 7-6 (7/3), 6-2.