ST. PETERSBURG, Russia - Former World No.2 Vera Zvonareva continues to turn back the clock in St. Petersburg.

The 34-year-old defeated No.3 seed Daria Kasatkina in straight sets on Friday, 6-3, 7-6(3), to book her spot in the semifinals of the St. Petersburg Ladies' Trophy. 

The Russian last reached a semifinal at a Premier-level event or higher at the WTA Finals in Instanbul in 2011, having recently returned to the Top 100 for the first time in six years. 

"It was a very tough match and Daria is a great player," Zvonareva said after the match. "I knew it was going to be very difficult, physically and mentally, and that I had to play my best tennis to beat her and it's great that I succeeded."

The current World No.97 has earned three victories over higher-ranked opposition this week, beginning with a first-round win over Ekaterina Makarova, and following with wins over No.5 seed Julia Goerges and now Kasatkina. 

Despite serving for the match twice in a second set which lasted over an hour, the veteran Russian was forced to win the match in a tiebreak after surrendering serve both times without arriving at match point. 

"It was very challenging in the first set, and I was up 2-0 in the second set, but she was fighting for every point," Zvonareva added.

"She came back, and I was serving for the match twice and wasn't able to win the games on my serve, but I did really well in the tiebreak. We both felt, I think, great support and it was nice that everyone came to watch our match. It's good that we have at least one Russian player in the semifinals."

Zvonareva advances to her second semifinal over the season, having also reached the last four to begin 2019 at the Shenzhen Open, and will face No.8 seed Donna Vekic, who scored an upset over top seed Petra Kvitova earlier on Friday.

"She's definitely one of the young and upcoming players. I think I played against her a very long time ago, when she was very young and we played on the grass," the veteran assessed. 

"I can't remember much of that match, so it's going to be a very tough challenge tomorrow."