Petra Kvitova had to dig deep to see off the challenge of Serena Williams and progress to the third round of the Cincinnati Masters after an absorbing contest in Ohio.
After suffering the worst defeat of her career to Johanna Konta in San Jose, Williams withdrew from the Rogers Cup for personal reasons, and later revealed she had been struggling with the emotional challenges of balancing motherhood with her career.
The 23-time grand slam singles champion produced an impressive performance in the WTA Premier 5 event, where she is a two-time winner.
But it was not enough to cope with an in-form Kvitova, who emerged a 6-3 2-6 6-3 winner after an entertaining struggle that lasted two hours on the outdoor hard courts of the Lindner Family Tennis Center.
"It's always a pleasure to share a court with her, I'm just happy I did well today," eighth seed Kvitova said.
"She really pushed me a lot, I just tried to stay focused on my serve."
While Williams has returned to the WTA Tour after giving birth last year, Kvitova has endured her own long road to recovery after being attacked with a knife during a break-in at her home in December 2016.
She said: "We all know how tough it is to come back, I couldn't imagine myself being in the top 10. There was a lot of hard work in the rehab and still a lot of things to do."
Kvitova did not take a step back in the opening set, the Czech preventing Williams from settling by dispatching a series of heavy groundstrokes that tested the movement of the returning veteran.
After consolidating a break earned in the fifth game, Kvitova later produced a powerful cross-court forehand from a demanding angle which Williams netted to give up her serve and the set.
It was the turn of Williams to assert herself in the second, the 36-year-old running Kvitova into the ground in a marathon game to take her fifth break-point opportunity, before fending off three in the next game to consolidate.
A second break followed in the seventh game, before Williams served it out to send the match to a third set.
The momentum swung once again in the decider, Kvitova breaking straight back after giving up her serve in the opening game, the 28-year-old rediscovering the movement and aggression that served her so well in the opener.
She secured a second break in the sixth game when Williams sent a backhand down the line long, Kvitova eventually sealing the victory after a pulsating struggle when a backhand serve return attempt from the American sailed long.
Williams opened the tournament in Cincinnati with a first-round win over Daria Gavrilova.
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