Toronto, ON, Canada, 12 August 2015 | AFP

Australia’s top-ranked player Sam Stosur has been knocked out of the WTA Rogers Cup in a first round loss to countrywoman Daria Gavrilova.

The Russian-born starlet swept Stosur aside in 78 minutes on Tuesday, prevailing 6-4 6-4 to move on to the second round, where she will meet Lucie Safarova.

Meanwhile, world No.1 Serena Williams rallied to advance to the third round by defeating Italy’s Flavia Pennetta 2-6 6-3 6-0.

Williams, winner of the past four Grand Slam events, took 98 minutes to capture her first match since winning at Wimbledon, and as she did during much of her title run in London, she did it after dropping the first set.

In the first set, Williams connected on only 44 per cent of her first serves, won just seven of 12 first serve points and only two of 15 on her second serve. She was broken four times, twice more than Pennetta.

But she held at love to open the second set and rolled to victory from there in the US Open hardcourt warm-up event, becoming the only player to reach the third round thanks to rain that washed out all but two matches on Monday.

Williams could complete a calendar-year Grand Slam with a victory at the US Open, which begins 31 August, and claim her 22nd career Grand Slam title, matching Steffi Graf’s Open Era record total.