Karolina Pliskova began her reign as world No 1 with a ragged 6-3 6-3 second round win over Anastasia Pavlyuchenkova on a blockbuster Wednesday when eight of the top 10 ranked players are in action at the Rogers Cup.

Pliskova, playing in her first tournament since her shock second round defeat at Wimbledon, struggled with a misfiring first serve and was guilty of some lapses in concentration. However, the lanky Czech was never seriously threatened as she disposed her 19th ranked Russian opponent in a tidy 70 minutes.

"I had a little bit (of nerves) before the match but during the match I felt much better especially at the end," Pliskova said in a courtside interview.

"I think it was not the best tennis from my side but I was trying to improve in the match.

"I'm definitely happy I am through to the next round, the first match is always tough."

Both sets followed a similar pattern, Pliskova surging to a 5-1 lead in the first and 3-0 in second. A loss of focus allowed Pavlyuchenkova to break and hold serve to trim the deficits.

But Pliskova snapped out of her brief funks each time and clinched her first win as No 1 with her seventh break.

A star-studded day on centre court began with Wimbledon champion Garbine Muguruza taming Belgian qualifier Kirsten Flipkens 7-5 6-2.

Despite a lowly ranking of 82nd, Flipkens represented a tricky first test for Muguruza with the Spaniard holding a slight 3-2 edge in their head-to-head meetings.

Muguruza, who had won only one match in her two previous visits to the Canadian hardcourt event, was tested during a topsy turvy opening set and served for the first set at 5-4 before double faulting to hand Flipkens a break.

The world No 4 hit back with a break of her own and then held serve to clinch the opening set, despite 30 unforced errors.

Muguruza looked much more like the player who dropped only one set on her way to the Wimbledon title after that and collected the early break in the second set to take control of the contest.

American teenager Catherine Bellis continued her brilliant form on the North American hardcourts by taking down eighth seeded Russian Svetlana Kuznetsova 6-4 7-5 to reach the third round.

The 18-year-old arrived in Toronto after reaching the semifinals in Stanford last week.

Kuznetsova was joined at the exit by her 16th seeded compatriot Elena Vesnina, who suffered a shock 6-3 5-7 6-4 loss to Australian qualifier Ashleigh Barty while Czech Lucie Safarova provided another upset by stopping 11th seeded Dominika Cibulkova 6-2 6-4.

VENUS BATTLES THROUGH

Venus Williams was forced to draw on all of her vast experience before overcoming Czech youngster Katerina Siniakova to reach the last 16.

The 37-year-old American ninth seed, who began playing on the professional circuit before 21-year-old Siniakova was even born in 1996, eventually prevailed 7-5, 7-5 in 1hr 39min.

It was a satisfying win for Williams, who shrugged off the failure to convert a string of break points to raise her game when it mattered late in the second set.

Williams, who will be chasing her third US Open crown next month after reaching the Wimbledon and Australian Open finals this year, said she had remained calm against Siniakova even when errors prevented her from taking control.

At one stage Siniakova saved eight consecutive break points to ensure she always remained in touch. Williams eventually converted only four of 13 break points.

"She played so well, so competitive," Williams said afterwards. "I had a few errors but I think the key is to keep going for it and hopefully you'll get some in at some point.

"On those points she played some great tennis. And what can you do except go back and try again," Williams said of Siniakova's multiple break-point saves.

Williams will now face Elina Svitolina in the next round.

Additional reporting by AFP