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.
|Teenager admits assaulting Wales great Thomas|
|Browns deny Condoleezza Rice is candidate for head coaching job|
|Koeman: Netherlands not favourites for Germany clash|
|Dalic ´not sad´ but blames fatigue for Croatia relegation|
|Proud Southgate hails England hero Kane as world´s best goalscorer|
|Last-gasp Exeter penalty try shatters Bristol|
|Mbappe dismisses talk of Cavani-Neymar rift|
|Keita will do ´great things´ for Liverpool – Mane|
|Mourinho needs time to fix Manchester United - Veron|
|Southgate sees progress as England reward loyal support|
|Miller hungry to ´knock out a Brit´ after Dinu demolition|
|Yasir, Hasan put Pakistan in control with five-wicket hauls|
|England´s resilience delights Kane as Three Lions secure Nations League Finals spot|
|Kane proves Nations League importance to England in Wembley decider|
|Muller, Hummels still important for Germany, says Low|
|Tevez in line for start in Copa Libertadores final second leg|
|England 2 Croatia 1: Kane able to secure Nations League Finals spot|
|It doesn´t sound real - Molinari stunned by 2018 exploits|
|Wales legend Thomas victim of alleged homophobic attack|
|Marquez crashes again as Dovizioso wins rain-interrupted Valencia GP|
|Warriors owner denies taking sides following Green-Durant spat|
|Alisson can become a global great, says Dida|
|The Sunday Seven - 7 Key Opta facts for NFL Week 11|
|Teen driver ´fine´ after sustaining spinal fracture in F3 crash|
|Willett wins first title since Masters triumph, Molinari tops Race to Dubai standings|
|Southgate overcomes ´stigma´ of being sacked to thrive with England|
|Anthony to Lakers ´not a question for myself´, says LeBron James|
|Warriors´ Stephen Curry staying ´cautious´ with injury recovery|
|Gunter hopes Bale can help family jet in to witness Wales record|
|Root pleased to practice what he preached|
|Tianjin Quanjian threaten action after Modeste returns to Cologne|
|I had to stop Kemba getting 70! – Jimmy Butler reflects on dramatic game-winner|
|Molinari wins Race to Dubai|
|Rooney: Some ex-players can´t come to terms with England doing well|
|In a spin: England´s win against Sri Lanka sets new record|
|Ogier wins sixth straight WRC title|
|Rogic, Kruse to miss Socceroos´ Lebanon friendly|
|Joerger has Kings´ ´full support´, says GM Divac|
|England seal series win over Sri Lanka|
|Butler´s heroics spoil Walker´s 60-point game as 76ers beat Hornets|
|He´s an honest guy – Djokovic defends Zverev after Finals controversy|
|Bonucci boos a ´mistake´ by fans, says Mancinima|
|Ronaldo still part of Portugal squad – Santos|
|Santos satisfied as Portugal reach Nations League Finals|
|Howell holds onto RSM Classic lead|
|McLeish optimistic as Scotland zero in on Nations League promotion|
|Luis Enrique rejects criticism of Spain star De Gea|
|Schmidt dismisses Hansen´s Ireland World Cup favourites claim as ´banter´|
|There are always imbeciles – Bonucci hits back at fans after frosty San Siro reception|
|Portugal draw ´a step forward´ despite poor finishing – Mancini|
|Ireland were just too good - Read|
|Thomas at the double as France end losing streak|
|Albania 0 Scotland 4: Forrest double sets up promotion showdown|
|Italy 0 Portugal 0: European champions outplayed but secure Finals spot|
|Sensational Djokovic marches into final|
|Stander lauds Ireland´s ´unreal´ defence as All Blacks are thwarted|
|Dazzling Ireland claim historic All Blacks scalp in Dublin|
|Federer unimpressed with Zverev boos|
|Let´s get it on! Cheika relishing England clash|
|Croatia coach Dalic to speak with Lovren over Ramos remarks|
|Xhaka puts improved form down to ´freak´ Emery|
|De Gea not lacking confidence, says Spain´s Saul|
|Jordan goalkeeper scores from own penalty area in friendly against India|
|Pollard leads Springboks to Murrayfield victory|
|Fired-up Japan taught England a great lesson - Jones|
|Sarries leave it late to down Sale, Bath and Saints win|
|O´Shea fumes at disallowed Italy try|
|Southgate welcomes England selection quandary|
|Reaching Rooney´s England goals record ´definitely possible´ – Kane|
|Debut try for Cokanasiga as England rally to avoid Japan upset|