World number one Serena Williams required two sets to reach the Rogers Cup semi-finals, while second seed Simona Halep celebrated a milestone victory over Agnieszka Radwanska in Toronto.

Three-time champion Williams posted a 6-4 6-3 win over Italian Roberta Vinci at the WTA Premier hard-court event on Friday.

Williams - winner of the Rogers Cup in 2013, 2011 and 2001 - tallied 12 aces and claimed three breaks of serve as she closed out the match in one hour, 18 minutes.

The American has now won 31 consecutive sets against players with one-handed backhands, having not tasted defeat since losing to Justine Henin at the 2007 US Open.

"I definitely feel it's another step in the right direction," Williams said.

"I don't feel like I'm at my best or anywhere near it, but I'm going in the right direction."

Awaiting Williams in the semis is Swiss starlet Belinda Bencic, who upstaged fifth seed Ana Ivanovic 6-4 6-2.

Bencic stunned Eugenie Bouchard, Caroline Wozniacki and Sabine Lasicki en route to the quarter-finals and the 18-year-old continued her giant-killing run at the expense of her Serbian opponent.

Romanian Halep is on track to meet Williams in the tournament decider after she rallied to beat sixth seed Radwanska 0-6 6-3 6-1 - her 300th career win.

After being completely outplayed by the Pole in the opening set, Halep won nine of the last 10 games to wrap up the milestone victory in resounding fashion.

"At the beginning I couldn't move my legs. I just felt very tired. And she was playing amazing - I couldn't do anything," Halep said.

"But I just kept focusing on what I had to do on the court - I knew I had to change my tactics, so I just kept the ball inside the court more and made more rallies out there."

Italian 15th seed Sara Errani earned a final-four showdown with Halep courtesy of a 6-4 6-4 triumph against Ukrainian qualifier Lesia Tsurenko.