Even a rain delay barely slowed defending champion Serena Williams in her barnstorming victory over Samantha Stosur at the Toronto Masters.

Three years after falling to Stosur in the US Open final, Williams exacted brutal revenge with a 6-0 6-2 second-round mauling on Wednesday in Montreal.

The World No.1 seized the first set and they were knotted at 1-1 in the second when rain halted play.

The American showed no ill-effects when they returned to the court, wrapping up the victory over the unseeded Australian in 58 minutes.

Williams stretched her career record over Stosur to 7-3.

French Open champion Maria Sharapova had to rally for a three-set victory over Garbine Muguruza to reach the third round.

The fourth-seeded former world No.1 fought back to beat the rising Spanish talent 4-6 6-3 6-1 to set up a meeting with another Spaniard, Carla Suarez Navarro, who was a 6-1 3-6 6-3 winner over Czech Karolina Pliskova.

Sharapova, playing her first match since a surprise fourth-round exit at Wimbledon, was a runner-up at this event in 2009 when it was held in Toronto.

“It’s been a few weeks since I’ve been in that competitive atmosphere,” Sharapova noted.

“It’s always quite different, no matter how much you train, you try to prepare for that.”

Meanwhile, sixth-seeded German left-hander Angelique Kerber made short work of France’s Caroline Garcia 6-4 6-1 and 11th-seeded former world No.1 Caroline Wozniacki steamrolled Czech Klara Koukalova 6-1 6-2.

Williams next faces 15th-seeded Czech Lucie Safarova, a 6-4 6-2 winner over Slovakian Magdalena Rybarikova.