Tennis: Caroline Wozniacki stuns new world No. 1 Karolina Pliskova in Toronto

Karolina Pliskova of the Czech Republic in action against Caroline Wozniacki of Denmark during the quarter-finals of the Rogers Cup Women's tennis tournament in Toronto, Canada, on Aug 11, 2017.
Karolina Pliskova of the Czech Republic in action against Caroline Wozniacki of Denmark during the quarter-finals of the Rogers Cup Women's tennis tournament in Toronto, Canada, on Aug 11, 2017. PHOTO: EPA

TORONTO (AFP) - Caroline Wozniacki survived three rain delays to book her spot in the WTA Toronto tournament semi-final with a marathon 7-5, 6-7 (3-7), 6-4 victory over world No. 1 Karolina Pliskova on Friday.

The sixth-seeded Wozniacki posted her first career win over a No. 1 player in seven tries as she blasted eight aces in the 2hr 56min centre court match.

She next faces American Sloane Stephens, who saved three match points in the third set to oust Lucie Safarova 6-2, 1-6, 7-5 in their quarter-final.

Pliskova fired five aces but won just 45 per cent of her second-serve points.

"I just tried to stay steady, tried to take the ball on the rise and try to stay aggressive when I could and keep my serves aggressive too," said Wozniacki.

Her record against No. 1s included five losses to Serena Williams and one to Dinara Safina.

Pliskova started quickly by winning five of the first six games of the first set which was delayed at the start by rain.

Wozniacki then started to assert herself on defence and offence, moving Pliskova around the court to win six straight games to take the first set.

Pliskova never recovered from that first-set loss. From then on, it was a matter of Wozniacki wearing her opponent down by keeping the ball in play.

"I think the biggest mistake was in the first set - so because of that, I think I lost," Pliskova said. "Overall, the match was much longer than just the hours on the court.

"It's just tough to play her in these conditions. She's putting everything back, so obviously, I did some mistakes."

Wozniacki will have her hands full with Stephens, who reached the quarter-finals with wins over third seed Angelique Kerber and two-time Wimbledon champion Petra Kvitova.

Stephens won the last four games and saved three match points to oust Safarova.