ST. PETERSBURG, Russia – Kristina Mladenovic continued her stunning run at the St. Petersburg Ladies Trophy with another shock victory, this time in the quarterfinal over the reigning champion, Roberta Vinci, 6-1 6-4.

The unseeded world No.51 continued with the approach that had seen off Venus Williams in the surprise of the second round. She tore into the 33-year-old’s serve in the first set, winning all three of the Italian’s service games. Facing set point at 30-40 in the final game, Vinci produced a wonderful drop shot down the line from deep in the court to take it to deuce, but Mladenovic was undeterred and came through for a 6-1 win.

A rocket of a return from @KikiMladenovic! @Formula_TX pic.twitter.com/2eXZkScAly

— WTA (@WTA) February 3, 2017

Vinci, facing Mladenovic for the first time since the 2015 US Open, faced break point once again at the start of the second set. This time, though, she proved more resilient and held for the first time in the match.

“Roberta is a big fighter,” said the 23-year-old of a more even second set, “and she is very smart on the court. She tried different tactics and almost turned it around in the second set. I’m happy I stayed calm and all the time responded with a game plan as well.”

The second serve increasingly proved key. Mladenovic won 50% of the points behind hers in contrast to 25% for Vinci and, although the French player served three double faults to her opponents’ one, it was that one that was crucial. A double fault from Vinci at 30-40 and 4-4 in the set gave the underdog the chance to serve for a meeting with Russia’s Natalia Vikhlyantseva in the last four.

Wonderfully delicate touch from @Roberta_Vinci! ? pic.twitter.com/LU8a5BBLaR

— WTA (@WTA) February 3, 2017

Mladenovic grew more aggressive, coming forward more with the win in sight. Serving at 5-4 she rushed too quickly to the net and gave up three break points. However she showed great composure to save all three. In a tense finale, the pair went to deuce four times before, at the third time of asking, Mladenovic converted match point with a top-spin heavy cross-court winner to qualify for her third career Premier semifinal.

“We played against each other last year in Hertogenbosch on grass and I won in three sets,” she said of Vikhlyantseva. “I discovered this young lady there for the first time and I thought she had an amazing great quality and game and potential for the future. I’m not surprised at her improvement and her ranking climbing up.”

Meanwhile the defeated champion said: “It was a difficult match, a tough match. Kiki played incredible tennis first set. In the second set I started to play much better than in the first – a bit more aggressive – I had some chances to break her, but she played too good. I played so so – this is tennis! I’m happy I managed to make it back to the quarter-final.”