ST. PETERSBURG, Russia - Reigning Roland Garros champion Jelena Ostapenko went toe-to-toe with a blast from the past in former World No.2 Vera Zvonareva, emerging victorious, 7-6(6), 6-3, at the St. Petersburg Ladies Trophy to reach the quarterfinals.

"It wasn't an easy match today; she played really well. In the first set I was down a break with her serving for the set, but I'm really glad I came back. I fought for every point."

The 20-year-old Latvian withstood a blistering start from Zvonareva to edge through the opening set in a tie-break after falling behind 3-5 to start, and held off a late surge in the second to clinch victory after one hour and 39 minutes on court.

"I think I was fighting, staying focused on every point. That helped me a lot. Plus, I served really well."

Ostapenko returns to St. Petersburg a very different player than the one who took home her maiden WTA doubles title with Alicja Rosolska a year ago, having won her first Grand Slam title and earned a career-high ranking of No.6 after last week's Australian Open.

Across the net was Zvonareva, who made back-to-back major finals in 2010, but took two years away from tennis to marry and give birth to daughter Evelyn. The 33-year-old Russian's comeback picked up steam in the fall, when she made the final of the WTA 125K event in Dalian and the semifinals of the Tashkent Open.

In all, it was Ostapenko's hyper-aggressive mindset that won the day, striking 35 winners to Zvonareva's four, and winning 70% of points starting on the Russian's second serve.

"I had a little injury after the Australian Open, so I took more than seven days off. I had some practice a couple of days before coming her. I think I was playing pretty well given it was just a couple days of practice."

Up next for the No.2 seed is either two-time Wimbledon champion Petra Kvitova or Romania's Irina-Camelia Begu.

"I really like this tournament and especially the city. I have a lot of relatives here; my mom's sister lives here. I get to see her and my family, and the tournament on the whole is very well-organized.  I'm really enjoying my time here."