Latest from the world of tennis: Serena rolls on, Halep struggles

Serena Williams took another step toward her fourth Rogers Cup title after dispatching Andrea Petkovic 6-3, 6-2 on Thursday to advance to the quarter-finals.

Williams, who won the title in 2001, 2011 and 2013, dominated on service and blasted nine aces in a match that lasted just over an hour. "I think I served better. That was the big difference," Williams told reporters. I still think I have a tremendous amount of improvement to do off the ground and everywhere else."

Williams will now take on Roberta Vinci of Italy, who beat Daria Gavrilova 6-4, 6-3.

Halep struggles with serve but edges past Kerber

Second seed Simona Halep struggled to overcome a predictably tough examination from Angelique Kerber before prevailing 6-3, 5-7, 6-4.

Both players found it difficult to hold serve, with the world number three Halep breaking the 11th ranked German's delivery nine times, while the Romanian was broken eight times herself.

But Halep, runner-up at the French Open last year, did just enough to eliminate the 13th seed and advance to the quarter-finals against Agnieszka Radwanska, who beat France's Alize Cornet 6-2, 4-6, 6-2.

It was a bad day for German players, with Kerber's compatriots Sabine Lisicki and Carina Witthoeft also shown the exit door.

Swiss teenager Belinda Bencic beat Lisicki 6-1, 1-6, 7-3(3) in a battle between unseeded players that lasted more than two hours.

Ukrainian Lesia Tsurenko beat Witthoeft 6-3, 6-4, while Italian Roberta Vinci took 78 minutes to dispose of Russian Daria Gavrilova by the same score.

Djokovic advances to cheers

World No 1 Novak Djokovic, second seed Andy Murray and three-time champion Rafael Nadal were all cheered into the quarter-finals of the Rogers Cup on Thursday while controversial Australian Nick Kyrgios exited to boos and a hefty fine.

Djokovic, also a three time winner on the Canadian hardcourts, needed only 54 minutes to complete a 6-2, 6-1 demolition of American Jack Sock while Murray was equally economic in disposing of Luxembourg's Gilles Muller 6-3, 6-2 in just over an hour.

It was all calm on centre court where Djokovic got off to a sluggish start but after breaking to go up 3-2 the 28-year-old Serb was in complete control with the Sock managing just a single break chance, which he was unable to convert.

"At the beginning of the match I think we were both a bit rusty," said Djokovic. "But I just managed to make the crucial break. That was the turning point, going up 3-2 in the first set. Then I was in control."

Djokovic continues to dominate at the ATP Tour's biggest events, running his Masters 1000 winning streak to 28 matches.

Nadal, finding his hardcourt footing coming off a clay court win in Hamburg, produced a snappy 6-3, 6-3 victory over Russian qualifier Mikhail Youzhny as Japanese fourth seed Kei Nishikori rolled to a 6-4, 6-4 win over 13th seed David Goffin.

While there were plenty of cheers in be heard across the Montreal tennis complex on Thursday few were for Kyrgios who entered his match to boos and exited the same way after falling 7-5, 6-3 to big-hitting American John Isner.

Murray beats Murray in Montreal doubles

Jamie Murray earned family bragging rights when he and his doubles partner defeated younger brother Andy at the Rogers Cup in Montreal on Thursday.

Doubles specialist Jamie Murray and Australian John Peers edged Scotsman Andy Murray and Indian Leander Paes 6-4 7-6(9).

Andy, who is third in the singles world ranking, likes to play doubles occasionally but does not particularly enjoy playing his brother, whose livelihood depends on doubles.

"It's not ideal, not a situation I want to be in all of the time," Andy told reporters after the brothers met competitively for the first time.

"Doubles is Jamie's career. I support him every single week. I watch all of his matches online. I'm always desperate for him to win.

"I want to play well for Leander too. It's tricky."

Andy's doubles defeat came just a few hours after he easily won his third-round singles match against Gilles Muller in straight sets, 6-3 6-2.