Saint Petersburg, Russia: Stan Wawrinka beat last year's St Petersburg champion Damir Dzumhur in straight sets to reach the semifinals on Friday.
The 33-year-old Swiss wild card beat the Bosnian, who was seeded sixth, 6-3, 6-4 in one hour and 11 minutes to level their head-to-head record at one all.
"The level of my play was good today and the win makes me feel positive," Wawrinka said.
In the last four, Wawrinka will face Slovak Martin Klizan, the 2012 champion, who battled back from a set down to beat seventh-seeded Denis Shapovalov of Canada 3-6, 7-5, 6-3.
"I expect an interesting match with Klizan in the semis," Wawrinka said. "We've played a couple of times in the past and it was always really tough."
Wawrinka, the former world number three who is down at 88 after struggling to find his best form following two operations on his left knee, looked nervous at the start dropping his serve early in the opening set.
He responded by breaking back twice to take the opener in 32 minutes.
In the second, Wawrinka broke early and experienced few troubles.
Earlier on Friday, fifth seeded Spaniard Roberto Bautista Agut saw off Italian third seed Marco Cecchinato of Italy 7-6 (7/0), 6-3 in the pair's first ever meeting.
In the semis, the 26-year-old Bautista Agut will face the winner of the match between Austria's French Open runner-up Dominic Thiem, the top seed, and the local crowd favourite Daniil Medvedev, who is seeded eighth.