SYDNEY - Tsvetana Pironkova's stretched her Sydney International winning streak to 14 matches with a straight sets victory over Barbora Zahlavova Strycova to reach the semi-finals on Wednesday. The Bulgarian, who again had to fight her way through qualifying to reach the main draw, ousted the world No.25 Czech 6-4, 6-1.

It continued an amazing run at the tournament by the Bulgarian world No.67, who was a shock winner in 2014 after battling through the three rounds of qualifying to beat Germany's Angelique Kerber in her eighth match at Sydney Olympic Park. Pironkova, 27, has once again had to do things the hard way to reach the last four after coming through qualifying to reach the main draw.

"I'm super excited. To be honest, I didn't really believe that I could go this far again because I had to start from quallies again," Pironkova said. "It's obviously a very hard thing to do considering the quallies nowadays is not like it was 20 years ago. It's also a very strong tournament. So I'm incredibly happy that I'm here today winning again, so I will just try to do it again," she said.

Pironkova said as the defending champion she was annoyed not to receive a wildcard into the main draw of the tournament. "I was hoping that I would get. I applied but obviously didn't get it," she said. "I was a bit disappointed about that. Not a bit, a lot disappointed obviously."

Last year's win in Sydney is the only WTA success of Pironkova's career. Pironkova now faces two-time Wimbledon champion and second seed Petra Kvitova in a repeat of their semi-final match-up last year which the Bulgarian won. Kvitova fought back to oust Australia's Jarmila Gajdosova 4-6, 6-3, 6-4 in a night match.

World No.22 Karolina Pliskova also won through to the semi-finals after seeing off Spain's Carla Suarez Navarro, 4-6, 6-4, 6-0. The 22-year-old from the Czech Republic now faces Angelique Kerber for a place in Saturday's final. Kerber, who had an early morning finish in the previous second round, recovered to overcome Spaniard Garbine Muguruza 0-6, 6-1, 6-4.

Del Potro ousts top seed Fognini: Defending champion Juan Martin del Potro came from a set down to dump top seed Fabio Fognini out of the Sydney International and advanced to the quarter-finals. The Argentine Grand Slam champion has won his first two matches in 10 months at the tournament following wrist surgery as he fights his way back to the top echelon of men's tennis. Del Potro, a one-time world No.4 but whose ranking has dived to 338 due to his inactivity, defeated the world No.18 Italian Fognini 4-6, 6-2, 6-2.

"I thought I played better. I feel better on the court, especially in the end of the match," said del Potro, who defeated Ukraine's Sergiy Stakhovsky in Tuesday's opening round. "I serve well, I hit good forehands, and my backhands improved from yesterday to this match a little bit. I need to keep playing with these guys, hitting the ball as fast I can and keep trying. My wrist is the same. It's not getting worse, so I have confidence with that. Of course I'm very happy to beat my first top 20 player of the year."

The former US Open champion will meet Kazakhstan qualifier Mikhail Kukushkin, who upset Uruguayan sixth seed Pablo Cuevas 7-5, 7-5 in the last eight. Second seed David Goffin also followed Fognini out of the tournament, after losing to Italian Simone Bolelli. Bolelli downed the Belgian 6-3, 6-3 and next faces Serbian qualifier Viktor Troicki in the last four. Troicki eliminated Spaniard Pablo Andujar 4-6, 6-3, 6-3.

German Philipp Kohlschreiber became the third top seed knocked out on Wednesday when he fell in straight sets to Australian Bernard Tomic 6-3, 6-4. Tomic will play Gilles Muller in the quarters after Muller defeated French seventh seed Jeremy Chardy 2-6, 7-6 (7/1), 6-4.