Elina Svitolina moved a step closer to back-to-back WTA Rogers Cup titles, while Simona Halep reached the semi-finals.

Defending champion Svitolina rallied to beat 14th seed Elise Mertens in straight sets in Montreal on Friday.

World number one and top seed Halep steamrolled Caroline Garcia after overcoming a difficult test.

US Open champion Sloane Stephens and Ashleigh Barty also advanced to the final four of the tournament.

SVITOLINA OVERCOMES DEFICIT

Ukraine fifth seed Svitolina survived to beat Mertens 7-5 6-3 on Friday.

Svitolina was down 4-0 in the first set before rallying to oust the Belgian in their quarter-final clash thanks to 25 winners.

"I think [Mertens] started pretty well," said Svitolina, who avenged her Australian Open quarter-final defeat.

"She was striking the ball and everything was going in for her. I just had to accept and move from there. I was just trying to stay longer in that set. I think it really helped me to get back my rhythm, and then I was just going more and more for my shots. I think this was the key."

Standing in the way of Svitolina and another Rogers Cup final is Stephens.

STEPHENS CRUISES INTO SEMIS

It was a straightforward match for third seed Stephens, who swept past Anastasija Sevastova 6-2 6-2.

Stephens hit 18 winners, served at 75 per cent throughout and converted five of nine break points to reach back-to-back Rogers Cup semis.

"I've been playing well and it's a good start here to the US Open Series. I'm happy to be back in North America and playing on hard courts, and I'm hoping for some more good results," Stephens said.

HALEP SHOWS CLASS TO SEE OFF GARCIA

A fourth successive Rogers Cup semi-final beckons for Halep after the Romanian star defeated Garcia 7-5 6-1.

Halep overcame a challenging opening set to blitz the Frenchwoman in 88 minutes.

"The first set was really tough," Halep told reporters. "I just didn't give up at all in the first set. After I took it, I felt more confident. I felt that I'm moving better, I'm playing better, stronger. [Garcia] went a little bit down with energy after she lost that set."

Barty awaits after the Australian beat Kiki Bertens 6-3 6-1.