SAN DIEGO, Calif. -- Donna Vekic advanced to her third quarterfinal of the season after defeating former No.1 Karolina Pliskova 6-3, 6-2 in the second round of the San Diego Open.

The victory snapped Vekic's six-match losing streak to the Czech, with her only win over Pliskova coming more than a decade ago in qualifying at the 2012 US Open. 

Now ranked No.77, the Croatian has enjoyed a strong run of form during the fall season. Vekic opened her San Diego campaign by tallying her first Top 10 win of the year over No.7 Maria Sakkari. 

"I think all the hard work is finally paying off," Vekic said. "I think this week and in Tallinn I started to believe in myself a little bit more, just going for my shots. It's something I wasn't doing during the U.S. swing. I did all the hard work, I've done all the right things in practice. It was kind of coming in the match in New York but in the important points I didn't go for it, I didn't trust myself. That's what I started to do in the last couple of matches and it's paying off."

Vekic capitalized on Pliskova's poor serving day to break the Czech's serve six times over the 74-minute match. Pliskova served at 66% in the match but won just 48% behind her first serve and 41% behind her second serve. Vekic out-aced her 6 to 2 and notched 17 winners to Pliskova's 16. 

"I think my movement is much better than a couple of months ago," Vekic said. "I definitely feel fitter as well. To have that confidence in my body, to be able to stay on court as long as possible, to know that I can get those shots. I played four matches now. I'm definitely happy to have a day off tomorrow."

San Diego will be her second straight quarterfinal, having reached the same stage at the Tallinn Open two weeks ago, where she lost to Belinda Bencic. Vekic will face either Aryna Sabalenka or Sloane Stephens for a spot in her first semifinal of the season. 

"I think it will be very tough to overhit Sabalenka if I have to play her," Vekic said. "I think I have a pretty good head-to-head with both of them. I love watching Sloane play. She's one of my favorite players to watch, she hits the ball beautifully. If it's against her I'm really going to enjoy that."