Top-ranked Simona Halep lost to Karolina Pliskova 6-4, 6-3 in the Madrid Open quarterfinals on Thursday, while Maria Sharapova also bowed out to Kiki Bertens.

Halep was the two-time defending champion and on a 15-match winning streak at the clay-court tournament. But Pliskova gave the Romanian no chance, breaking her serve four times and hitting 20 winners.

"I think I played one of my best matches this year for sure, and for sure on clay in my life," the sixth-seeded Pliskova said. "I feel amazing since in the last six matches I lost to her. I never thought I would beat her. My serve was great and everything went my way."

Halep got off to a great start by breaking Pliskova for a 2-0 lead, only for the Czech to take the break right back to swing the match in her favor.

"I missed in some important moments. That's why it went her way," Halep said. "I'm not upset. I'm not looking in a negative way. I won two times here. I played great matches. So I take the positives."

Pliskova's only prior victory from her previous seven matches against Halep was in the 2016 Fed Cup.

She arrived in Madrid fresh from winning her 10th career title in April, when she was victorious on clay in Stuttgart.

Pliskova is now the highest seeded player left in the women's tournament after both No. 2 Caroline Wozniacki and third-seeded Garbine Muguruza lost Wednesday. Pliskova beat Victoria Azarenka and Sloane Stephens in previous rounds and has recorded nine wins in a row.

She will play Petra Kvitova or Daria Kasatkina in the semifinals.

Seventh-seeded Caroline Garcia also advanced to the final four after beating Carla Suarez Navarro 6-2, 6-3.

Garcia will take on Bertens after she came from behind to beat Sharapova 4-6, 6-2, 6-3. Bertens finished Sharapova off when the Russian's backhand missed on a second match point.

In the third round of the men's tournament, Dusan Lajovic fought back from 0-4 in the decisive tiebreaker to stun fourth-seeded Juan Martin del Potro 3-6, 6-4, 7-6 (6) for his first career win against a top-10 ranked player.

Lajovic moved on to meet sixth-seeded Kevin Anderson, who advanced to the quarterfinals after eliminating Philipp Kohlschreiber 6-3, 7-6 (7).

Kyle Edmund continued his excellent run in Spain by ousting eighth-seeded David Goffin 6-4, 6-4. Edmund, an unseeded Brit, defeated former No. 1 Novak Djokovic in straight sets on Wednesday.

Edmund will face 19-year-old Denis Shapovalov, after he defeated Milos Raonic 6-4, 6-4 in an all-Canadian clash.

Novak stay optimistic

Novak Djokovic is trying his best to stay optimistic despite a disappointing start to his season.

Former No 1-ranked Djokovic has struggled since returning from a layoff for a right elbow injury and is yet to reach the quarterfinals in the six tournaments he has played this year. His latest defeat was against Kyle Edmund in the second round of the Madrid Open on Wednesday.

"Obviously I'm disappointed from losing this match, but I can be happy with the progress of the level of tennis," Djokovic said. "There are positives to take out from this. But obviously disappointing to go out early in the tournament."

Djokovic lost in the third round in Monte Carlo a few weeks ago, following second-round exits at both Miami and Indian Wells.

"It's a process," Djokovic said. "It's something I have to accept, I have to embrace. In general I feel much better about everything that is happening on the court and around tennis in general ... than maybe two months ago."

In a bid to get back on track, Djokovic has reunited with coach Marian Vajda and trainer Gebhard Gritsch after stints working with former players Andre Agassi and Radek Stepanek. "If there is anybody that knows my game well, knows me as a person well, especially in the last decade, it's these two guys," Djokovic said following his first-round in Madrid.

Halep, Sharapova both lose in Q/F