TORONTO, Canada - No.3 seed Karolina Pliskova was dragged into a dogfight despite a dominant start against the determined qualifier Alison Riske - but righted the ship to win their Rogers Cup second round clash 6-4, 6-7(4), 6-2 in two hours and three minutes.

The result extends the former World No.1's mastery of her head-to-head against Riske: she has now won six straight matches in the series to lead 7-1 overall, and has not lost to the American since 2012, at an ITF event in the Bronx. But today's passage into the third round was far from straightforward - although for a set and a half, as Pliskova clinically made her way to a 6-4, 4-1 lead, it appeared as if it might be.

"We always have tough matches together, so I knew it was going to be tough," Pliskova said after the match.

"It looked easy, I think for a set and a half, and I think I was too relaxed in the middle of the second. She just came up with some good serves, some good shots.

"It was tough in the second set, but after [I put in] just a little bit of energy, I went with good shots and good serves and it was much better in the third set."

Until that point, the 27-year-old had been a service machine. Nine of her 11 aces came in that stretch, and Pliskova was able to pull a big first serve out of her pocket to save all five break points she faced - much to the frustration of her opponent, who was unable to put the return in court on four of those occasions.

Riske did manage to stick with Pliskova for most of the first set, but had been less reliable off the ground throughout, particularly on a forehand wing that oscillated between bold winners and wild errors.

Serving to stay in the set, the 29-year-old was made to pay for these - and for an ill-timed first double fault on set point, the first time Riske had faced a break point in the match.

Rattled by the impenetrability of the Pliskova delivery and by confusion over an ambiguously stopped point in the fourth game of the second set, Riske found herself on the verge of defeat after Pliskova pressed home her advantage by upping the pace on return.

But advice from coach Billy Heiser to stay back when returning the Pliskova second serve paid immediate dividends for the World No.37.

Getting a proper hold of some returns for almost the first time in the match, Riske carved out yet another opportunity for herself - and finally, facing her seventh break point of the day, Pliskova cracked with her third double fault.

Riske has made a habit of unlikely fightbacks this summer: over the grass season, she won six out of a streak of eight three-setters that she played en route to her second career title in 's-Hertogenbosch and maiden Grand Slam quarterfinal at Wimbledon.

Her memorable season has continued in North America both on and off court: Riske's marriage last month to Stephen Amritraj was followed by another battling performance this week as she became the fourth player in 2019 to win two matches from match point down over Maria Sakkari in the first round.

With Pliskova now afflicted by unforced errors and mounting double faults, the stage was set for a tiebreak - the seventh the pair had contested.

Therein, it was Riske's turn to deliver a serving masterclass: Pliskova was able to make just one return, and her fifth double fault proved decisive as the game's only minibreak.

But the Brisbane, Rome and Eastbourne champion was able to gather herself swiftly as the deciding set got under way - while Riske was unable to sustain the momentum from her resurgence, instead returning to the error-littered baseline game of the first set.

Two double faults put her down a break in the third game; while Pliskova was also still struggling in this area as her own double fault total climbed to nine, the 2016 US Open runner-up was able to counter them with enough solid first serves to make her own service games rather more comfortable.

Another break followed for Pliskova in the seventh game, and - belying the struggle of the past two hours - the World No.3 came up with a strong hold to 15 to close out the win and set up a third-round clash with No.16 seed Anett Kontaveit, who had earlier progressed after Carla Suárez Navarro retired trailing 7-5, 3-1 due to a right hip injury.

"I've been practicing three weeks on hard, but the match is always something different. You have more nerves, more stress," Pliskova said.

"You just need to get used to it a little bit, because there was quite a big gap after Wimbledon. Every match is going to help me and it can only be better tomorrow.

"We played in Indian Wells and it was a tough match, for sure. She's a tough competitor. It's going to be similar to today. She's fighting, she's playing good tennis from the baseline. I think I have bigger weapons, but I still need to play well."