Stuttgart: German qualifier Laura Siegemund continued her clay court roll, backing up her first round upset of Anastasia Pavlyuchenkova with an even bigger upset of fourth seed Simona Halep to enter the quarter-finals of the Porsche Tennis Grand Prix late on Thursday.

Siegemund, who came through the qualifying rounds, took a little over an hour to send the Romanian packing 6-1, 6-2 and book her place in the last eight stages.

“I think it would be presumptuous to say the match was perfect, because there is always something to improve,” Siegemund told the official WTA website.

“But that win was very good and of course, I am mega happy. I had not expected that it would go so smoothly,” she added.

The odds were heavily in favour of the German girl as Halep has been nursing a left ankle injury that she picked up in Romania’s 1-4 loss to Germany in their Fed Cup encounter last weekend. Halep looked lame from the baseline with the fourth seed hitting only three winners and making ten unforced errors.

But Siegemund was undaunted by both the occasion and her ailing opponent across the net as she kept the home audience entertained with her forceful display for an easy win. “I just played point by point,” she said.

“Sure, it’s the biggest win of my career, but now after the match, I can only say, I have made few mistakes. I started very aggressively, and that was exactly my plan of attacking her serve and tearing open the field early,” she added.

With this win, Siegemund continues her upward momentum in women’s tennis. Earlier this year, she had defeated World No.22 Jelena Jankovic at the Australian Open, and in Charleston she made it to the quarter-finals of a premier-level event for the first time.

Siegemund will go on to play against Roberta Vinci in the quarter-finals after the Italian booked her spot in the last eight with an emphatic 6-3, 6-4 win over Julia Goerges.

Earlier, Petra Kvitova snatched victory from the jaws of defeat against Monica Niculescu to set up a quarter-final meeting with third seed Garbine Muguruza. Also advancing to the quarter-finals was Carla Suarez Navarro, with an impressive 6-2, 6-2 win over Anna-Lena Friedsam.

In the opening round, Kvitova had barely broken sweat in her straight sets win over Louise Chirico. But in Niculescu she faced a completely different test, as she trailed her opponent for most of the first two sets.

However, after winning a close tie-breaker in the second set, the former Wimbledon champion went on to win 2-6, 7-6 (5), 6-2 after nearly three hours on court.

Collated results from the fourth day of the WTA Stuttgart Open on Thursday (x denotes seeding):

2nd round

Agnieszka Radwanska (POL x1) bt Andrea Petkovic (GER) 1-6, 6-1, 6-2

Karolmna Pliskova (CZE) bt Ana Ivanovic (SRB) 6-4, 6-2

Laura Siegemund (GER) bt Simona Halep (ROM x4) 6-1, 6-2

Roberta Vinci (ITA x6) bt Julia Gvrges (GER) 6-3, 6-4

Petra Kvitova (CZE x5) bt Monica Niculescu (ROM) 2-6, 7-6 (7/5), 6-2

Carla Suarez (ESP x7) bt Anna-Lena Friedsam (GER) 6-2, 6-2