Stan Wawrinka took the hard road to his second win this week in St Petersburg, with the Swiss reaching the quarter-finals in Russian after going three sets with Evgeny Donskoy.
Wawrinka, a three-time Grand Slam champion advanced in an hour and three-quarters with seven aces and three breaks of serve.
The 35-year-old, a semi-finalist four years ago. held off five break points against his Russian opponent.
“It was a great match, tough opponent, but my level was better from the beginning, ” Wawrinka said.
“I’m happy to keep winning here. Great atmosphere, great people here tonight and happy to play in the quarter-finals.
“In the second he started to play a bit more aggressively. He was dictating a little bit more the game. It was tough.”
Wawrinka called the level of competition “great from both sides, I played a really solid match tonight,.”
Defending champion Daniil Medvedev sent over 22 aces to dominate his opening match after a bye, defeating one-time No. 7 Richard Gasquet 3-6, 6-3, 6-0.
The top-seeded Russian next takes on two-meter-plus American giant Reilly Opelka, who beat Croatian qualifier Nino Serdarusic 3-6, 7-6(5), 6-2.
Opelka added 26 aces to his rising season total of 328 untouchable serves.
Medvedev just avoided losing his third straight match after early exits in New York, Hamburg and Paris.