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.
|UEFA warns FFP cases can be re-opened based on ´new information´|
|Foakes to keep England place for second Test|
|WATCH: Rooney looking sharp in England training return|
|Mbappe: Money in football is truly indecent|
|Djokovic back to brilliant best as Isner is beaten|
|Celta Vigo replace Mohamed with Cardoso after Real Madrid defeat|
|Joshua intrigued by Usyk, says Hearn|
|Ibrahimovic beats Rooney to MLS Newcomer award|
|Rams WR Kupp out for season with torn ACL|
|Sturridge denies ever gambling on football following FA charge|
|Koeman understands De Ligt´s Eredivisie frustrations|
|Jimmy Butler trade: 76ers acquire Timberwolves star in blockbuster deal|
|´Improve your attitude´ - Deschamps issues Dembele warning|
|Sturridge charged with misconduct over alleged breach of betting rules|
|Saints sign Marshall following Bryant injury|
|Mendy suffers knee injury, leaves France squad with Lacazette|
|Zverev beats Cilic in error-strewn London battle|
|Rafinha replaces injured Casemiro in Brazil squad|
|´One-dimensional´ Australia batsmen need work before World Cup - Finch|
|Mancini keen to work with ´incredibly gifted´ Tonali|
|Italian manager of the year Allegri targets long Juve stay|
|Injured Lee departs as Wales prepare squad for Tonga|
|Conte content to wait until June for coaching return|
|Etzebeth set to return, Whiteley a doubt for Scotland Test|
|In-form Verstappen does not need distractions from 2019 challenge|
|FA asks Guardiola to explain Manchester derby referee comments|
|LaLiga MVP Messi hopes the division stays wide open|
|Murray and Henshaw out of All Blacks Test|
|Injured Man Utd duo Pogba and Martial drop out of France squad|
|Modric cannot always be the best - Dalic|
|Very troubling times - LeBron James alarmed by gun violence|
|Bayern confirm Ribery ´altercation´ with reporter|
|Madrid hit by injuries to Nacho and Casemiro|
|Record-breaking Mushfiqur torments Zimbabwe|
|Spartak Moscow appoint Oleg Kononov|
|Rooney predicts ´exciting time´ after being named in MLS Best XI|
|Former England call-up Graham replaces Thomson in Scotland squad|
|Slater and Thurston among Queensland greats to join Maroons staff|
|Rapana set for six months out after shoulder surgery|
|Alves determined to play in the Premier League|
|Rockets GM denies Anthony will be waived|
|Monaco´s plight not Henry´s fault - Silva|
|It´s like the FBI came - River assistant unable to talk to Gallardo during final|
|Norman says Washington home crowds ´just don´t really care´|
|Bucks beat Nuggets to finish gruelling schedule stretch|
|Madrid ´very happy´ with Solari, says Butragueno|
|Titans stun Patriots, Browns upset Falcons|
|Browns´ Chubb relishes record-breaking performance: It definitely is very special|
|MLS Review: Red Bulls, Atlanta to meet in conference finals|
|Neymar wants more from perfect PSG|
|Higuain is feeling a lot of pressure – Gattuso|
|I didn´t insult anyone, says apologetic Higuain|
|Allegri delighted with Juventus response|
|Kyle Busch wins at Phoenix as Harvick, Truex qualify for Championship 4|
|WATCH: Highlights of thrilling Boca-River Copa Libertadores final|
|PSG coach Tuchel demands more despite Monaco thrashing|
|Boca missed too many chances, rues Schelotto|
|Solari remains tight-lipped on Real Madrid future|
|Hamilton not surprised by Verstappen-Ocon collision|
|Ronaldo fires Juventus to Serie A record|
|Higuain did nothing serious - Ronaldo hopes Milan striker avoids ban|
|Solari completes perfect Real Madrid audition with fourth straight win|
|Verstappen ordered to do public service after Ocon scuffle|
|Nishikori stuns out-of-sorts Federer|
|Fitzgerald overtakes Owens in career receiving yards|
|Monaco 0 Paris Saint-Germain 4: Cavani hat-trick adds to Henry woes|
|Celta Vigo 2 Real Madrid 4: Solari leads Los Blancos to fourth straight win|
|AC Milan 0 Juventus 2: Higuain sent off in horror show|
|Brees leapfrogs Favre on all-time list for touchdown passes|
|Kuchar holds on to seal first title since 2014|