Djokovic and Williams get into North American groove

World number ones Novak Djokovic and Serena Williams both played their first competitive matches following their titles at Wimbledon last month. Djokovic's outing was less problematic than his counterpart on the women's circuit. He won in straight sets while 33-year-old Williams needed three to get past her fellow veteran Flavia Pennetta.

Serena Williams dropped the first set against Flavia Pennetta in the second round match at the WTA event in Toronto. USA Today Sports/Dan Hamilton

Djokovic and Williams marked their return to competition on Tuesday night with victories in the North American warm-up events before the US Open.

The final grand slam tournament of the season starts in New York on 31 August.

Williams, who is the defending champion, will be attempting to retain her crown and thereby become the first woman since Steffi Graf in 1988 to achieve a calendar grand slam.

When Williams triumphed at Wimbledon last month, she completed a 'Serena Slam' - crowns at four consecutive grand slam events.

She first pulled off that feat more than a decade ago. She claimed Roland Garros in Paris in 2002, Wimbledon, the US Open and the Australian Open of 2003.

All four trophies in the same year hasn't been accomplished since Graf's glory days nearly three decades ago.

But her preparations for a tilt at history appeared to be in severe trouble against Pennetta. Williams's serve was abject. Only 44 per cent of her first serves went in and she lost it four times.

There was a solid hold at the outset of the second set but after Pennetta levelled for 1-1, Williams again dropped her serve to trail 1-2.

But that setback appeared to set off the alarm bells and from there she won 11 of the next 12 games to take the second 6-3 and the decider 6-0.

It was the 725th victory on the circuit for the 33-year-old who withdrew from last week's Stanford event with an injury to her right elbow.

"The elbow was okay. It's definitely not perfect but I'll see how it recovers," she said after the 98-minute match.

"It was a good opportunity for me because I hadn't played a match on hardcourts since early April, after Miami. It was a long time ago."

Before turning her attentions to the US Open and the possibility of a 22nd grand slam singles title, Williams is aiming to win for a third time in Toronto following successes in 2011 and 2013.

Djokovic won the first of his three titles in Canada in 2007, beating Roger Federer in three sets.

The 28-year-old Serb disposed of the Brazilian Thomaz Bellucci 6-3, 7-6 to move into the third round.

It was Djokovic's first appearance since winning Wimbledon more than a month ago also at the expense of Federer. He also created a slice of personal history with his 250th win at a Masters 1000 event.

"It was a very intense match for both players," Djokovic said. "There was a lot of tension and a very high quality. But I managed to stay cool and mentally tough in the right moment."

In another milestone at the tournament - much to the chagrin of the partisans - the Canadian eighth seed Milos Raonic lost in straight sets to the Croatian Ivo Karlovic who hit the 10,000th ace of his career during the match.

The Croatian 36-year-old is only the second man to reach the mark. The first was another Croatian, Goran Ivanisevic. He eventually clocked up 10,183 aces over 895 matches.

Karlovic, who has passed the mark after 527 matches, admitted his former Davis Cup teammate’s record was in his sights.

“Of course, that is my goal,” he said. “I would hope that it will be this year. If not, it's OK, also if it's next year. Hopefully I will be able to do it, be healthy enough, and hopefully it will be soon.”