Serena hammers Petkovic

World number one Serena Williams continued her dominance over Germany's Andrea Petkovic with a 6-3, 6-2 victory in the third round of the WTA Rogers Cup on Thursday.

Top seed Williams hammered 28 winners and blasted nine aces to beat the 16th seeded Petkovic for the fifth straight time.

"I think I served better than in my first match. It was a big difference," Williams said.

"I still think I have a tremendous amount of improvement to do off the ground and everywhere else."

Williams, who never faced a break point and held all nine of her service games in the 62-minute match on center court, barely broke a sweat Thursday.

The 33-year-old American advances to the quarter-finals where she will face Roberta Vinci who snapped the win streak of rising star Daria Gavrilova with a 6-4, 6-3 win.

Williams has beaten Vinci in all three of their previous meetings, losing just 14 games in total.

Second seed Simona Halep smashed an ace on match point to defeat red-hot Angelique Kerber 6-3, 5-7, 6-4 and reach the quarter-finals.

Kerber had won seven in a row and was coming off her fourth title of 2015 after winning last week's Stanford tournament.