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.
|Barty upsets Kerber in Wuhan|
|England could still pick Cipriani despite training camp snub|
|Astros become first defending champions to reach 100 wins since 1990 Athletics|
|Wilder waiting for ´real offer´ to fight Joshua|
|LeBron focusing on patience after first Lakers practice|
|Pochettino expects Spurs in new stadium by Christmas|
|Inzaghi: With Ronaldo, Juve are best team in Europe|
|Some people talk too much – Icardi hits back at critics|
|Kovac, Robben praise Augsburg after draw|
|Angels star Ohtani to undergo Tommy John surgery|
|Simeone tips Gimenez to be fit for Madrid derby|
|Smith on his NBA Finals miscue: People make mistakes all the time|
|Rams CB Talib to have ankle surgery|
|Cousins ´feeling a lot better´, still unsure when he´ll return|
|I knew we´d be in trouble with Jones on penalties – Mourinho|
|Coyotes forward Galchenyuk expected to miss opener|
|Guardiola won´t compare Foden to Iniesta|
|Lampard shell-shocked as Derby win at Old Trafford|
|Ryder Cup 2018: USA celebrities take the honours|
|Manchester United´s torrid penalty shoot-out run continues against Derby|
|Guardiola: Foden already a great, great player|
|Atletico Madrid 3 Huesca 0: Rojiblancos cruise ahead of Madrid derby|
|EFL Cup: Lampard dumps out Mourinho, Burnley lose at Burton Albion|
|Mourinho denies Pogba row despite stripping midfielder of vice-captaincy|
|Fabinho situation not complicated, insists Klopp|
|Manchester United 2 Derby County 2 (Derby win 8-7 on pens): Lampard heaps pressure on Mourinho|
|Afghanistan snatch tie after Shahzad pummels India|
|Inter 2 Fiorentina 1: D´Ambrosio maintains Nerazzurri revival|
|Oxford United 0 Manchester City 3: Foden stars as EFL Cup holders cruise into round four|
|Cousin takes Gabon post after Aubameyang rejection|
|Bayern Munich 1 Augsburg 1: Neuer error costs champions|
|Paris Saint-Germain must be a Champions League force to help Neymar - Baptista|
|Salgado warns of ´war´ in Spanish football|
|Cech deserves Arsenal place, says Seaman|
|Halep and Garcia among seeds to fall in Wuhan|
|F1 Raceweek: Mercedes taking no comfort in points advantage|
|Benitez charged by FA for referee comment relating to Zaha treatment|
|Cibulkova dumps out hampered Halep in Wuhan|
|Mourinho questions his players amid reports Pogba won´t captain United again|
|European Ryder Cup diary: Fleetwood´s hair delights Poulter|
|USA Ryder Cup diary: Tiger´s roaring reception, McEnroe´s bold prediction|
|Loans to be limited under new FIFA proposal|
|Prolific Nadolo signs new Montpellier contract|
|Modric? For us, Messi is the best – Valverde|
|Murray makes winning start in Shenzhen|
|Mickelson would cherish first victory on European soil|
|Hodge hoping pressure proves too much for South Africa|
|Woodward in show of support for under-fire Mourinho|
|Mickelson jokes he wants ´a shot a side´ from Tiger in Thanksgiving showdown|
|Reed: Captain America is a villain in Europe|
|Duminy to captain Proteas as Elgar replaces injured Amla|
|No Tottenham timeline for Lloris, Vorm returns|
|Woods ready for ´awesome environment´ on Ryder Cup opening hole|
|Tony Bellew determined to prove doubters wrong against Oleksandr Usyk|
|Tuchel explains why he likes Neymar at number 10|
|Manchester United smash revenue record but profits down|
|Furyk downplays Ryder Cup pairings talk, says Tuesday is about individuals|
|Rejuvenated Tiger out to improve poor Ryder Cup record|
|Saunders fined £100,000 for ´sickening´ online video|
|Hazard can reach his full potential with Sarri´s Chelsea - Zola|
|Ryder Cup heading back in Europe´s direction, says Niall Horan|
|Wow! Klopp hails Sarri´s Chelsea transformation|
|Giovinazzi to partner Raikkonen at Sauber in 2019|
|Bjorn backs ´phenomenal´ Rahm to continue trend of Spanish success|
|Durant in no rush to decide Warriors future|
|Rossi to face anti-doping hearing|
|Mignolet to return for Liverpool against Chelsea|
|Premier League ´interesting´ for Germany boss Low|
|Wilder wins Twitter vote to be Joshua´s next opponent|
|BREAKING NEWS: Isco an El Derbi doubt due to appendicitis|