Portugal's Joao Sousa played the villain at the St. Petersburg Open on Thursday, upsetting second seed Karen Khachanov of Russia 7-6(2), 6-4 to reach the quarter-finals at the ATP 250.

The unseeded 30-year-old fell to Khachanov in their first FedEx ATP Head2Head meeting three years ago, at the 2016 Chengdu Open. But Sousa didn't drop a point on his serve in the first-set tie-break and broke in the fifth game of the second to advance.

“They were pushing Karen. They were pushing me as well so I think I played a great match. I think they enjoyed,” Sousa said. “Unfortunately, Karen couldn't win. He's the Russian playing at home. But in the end, I was able to win and I'm very happy.”

Sousa is through to his third quarter-final of 2019 and his first not on clay. In back-to-back weeks, the veteran right-hander made the quarter-finals in Bastad and the semi-finals in Gstaad. He will next meet Kazakh Mikhail Kukushkin, who beat Damir Dzumhur on Wednesday.

"Mikhail is a great player," Sousa said. "Hopefully tomorrow I will have a little bit more crowd [support]. It's going to be another tough match as [was] today. So now it's time to recover and to enjoy this victory."