Karolina Pliskova continues to settle in to her new role as world No.1, moving into the quarter-finals of the Rogers Cup after Japanese teenager Naomi Osaka was forced to retire with an abdominal injury.

The 19-year-old qualifier, ranked 50th in the world, had been giving Pliskova a mighty battle, winning a second set tiebreak, but then after being broken to open the third suddenly called for the trainer and soon retired trailing 6-2 6-7 (7-4) 1-0.

“She played well, especially in the second set she was fighting pretty hard, much better than the first,” Pliskova said.

“I was just trying to stay in the game, the first game of the third set was very tough, I didn’t even know she was injured.”

Pliskova will need to have her serve firing on all cylinders when she meets sixth seed and former world No.1 Caroline Wozniacki in the last eight.

In a battle of former-Rogers Cup champions, a ruthless Wozniacki showed no mercy by sweeping past her good friend and 10th-seeded Pole Agnieszka Radwanska 6-3 6-1 in just 78 minutes.

The only hiccup in an otherwise polished effort came when Wozniacki was up 5-0 in the second and squandered three match points.

The slip-up, however, only delayed the inevitable, the Dane closing out the match at the next opportunity with a stinging forehand winner.

“We’ve known each other since we were five and six years old so there are no secrets out there,” said Wozniacki, who has reached five finals this season without winning a title.

“It is always unfortunate to play a good friend in such an early round but at the same time it is part of the game.”

Czech Lucie Safarova also made the last eight by outlasting Russia’s Ekaterina Makarova 6-3 6-7 (7-3) 6-2, while France’s Caroline Garcia beat 18-year-old American Catherine Bellis 6-4 6-2.

World No.2 Simona Halep was far too strong for Barbora Strycova, who eliminated Australia’s Daria Gavrilova on Tuesday, winning 6-1 6-0.