Caroline Wozniacki and Sloane Stephens made their way through to the WTA Rogers Cup semi-finals, before rain stopped play in Toronto on Friday.

After three rain delays and almost three hours on court, Wozniacki eventually defeated world number one Karolina Pliskova 7-5 6-7 (3-6) 6-4.

Stephens became a WTA Premier 5 semi-finalist for the first time, saving three match points and winning the last four games to progress 6-2 1-6 7-5 over Lucie Safarova.

Garbine Muguruza managed to take the first set 6-4 over Elina Svitolina, but poor weather meant they could not finish the match.

Meanwhile, Carolina Garcia and Simona Halep failed to even step foot on the court.

Prior to Friday's win, Wozniacki was 0-6 in matches against the world's top-ranked player, having lost five times to Serena Williams and once to Dinara Safina.

Following a delayed start, Pliskova raced out to a 5-1 lead in the opening set but the Danish sixth seed managed to extend points and dig in, winning the final six games to snatch the set.

The second set somehow remained on serve, with the Czech first seed saving four break points in the fifth game.

Wozniacki was in rhythm and managed to continually apply pressure however, winning 81 per cent of points on her first serve in the second. She won 73 per cent of points on her first serve in total.

Pliskova still managed to secure a break in the fifth game of the deciding set, but Wozniacki scrapped to deny a double-break, holding from 30-30 in the seventh. The latter broke back in the eighth before she ran off the last four games of the match.

Stephens won in similarly dramatic fashion, leading at 3-1 in the third set before having to save three match points against Safarova.

In only her third tournament of the year, the American world number 934 continued her impressive run in Toronto, after victories over Angelique Kerber and Petra Kvitova.

Stephens is making up for lost time on the court at the Rogers Cup, though, with her four matches this week taking nearly eight hours in total.

Wozniacki and Stephens will face each other, but will need to wait before the other semi is finalised.