Carlos Alcaraz let loose his frustrations with a violent racquet smash in a 4-6, 7-6 (7/5), 6-4 upset opening loss to Gael Monfils on Friday at the ATP and WTA Cincinnati Open.
The reigning Roland Garros and Wimbledon champion could not match the wily skills of his 37-year-old French opponent, two decades in the game and a threat to any young gun.
Alcaraz, ranked third in the world, now heads to the US Open starting a week from Monday without a hardcourt win and only one second-round summer cement match in his legs.
The Spaniard lost the Cincinnati final last year to Novak Djokovic.
Alcaraz committed 40 unforced errors while Monfils had 48 in victory along with 15 aces in a match halted by rain Thursday night during the tie-breaker.
While the frustrated second seed was fuming at his form and occasionally screaming at his team, world No 1 Jannik Sinner celebrated a quiet 23rd birthday, with fate handing him a present in the form of a walkover.
The Italian advanced effortlessly into the quarters when Australian opponent Jordan Thompson withdrew before their match with a rib injury.
Sinner now gets a rematch of last week's quarterfinal in Canada, which he lost to Andrey Rublev. The Russian finished a rain-delayed match over Brandon Nakashima 7-6 (7/5), 6-1 on Friday.
Rain delayed play until early afternoon, with Alcaraz coming out after a 90-minute delay in hopes of finishing off Monfils after winning the first set but trailing in the tiebreaker from the night before.
But the Frenchman had another agenda, with Monfils taking the breaker to level the sets and breaking Alcaraz for 2-1 in the third.
Monfils double-faulted in his first match point but sent a winner deep into the corner on his second chance to clinch victory.
The number 46 began the week here by knocking out surprise Montreal winner Alexei Popyrin of Australia.
Fifth seed Alexander Zverev advanced into the last eight over Spain's Pablo Carreno Busta 7-5, 7-6 (8/6).
The poor run of form for seventh seed Casper Ruud continued as the Norwegian went down 6-3, 6-1 to Felix Auger-Aliassime in 68 minutes, with the Canadian sending down 14 aces.
NO.1 SWIATEK CRUISES
Women's top seed Iga Swiatek defeated Marta Kostyuk for the second time this season, powering into the quarterfinals by 6-2, 6-2.
The Pole backed up her win over the Ukrainian at Indian Wells last March and now stands 3-0 in the rivalry without the loss of a set.
Due to the morning of rain, Swiatek stepped onto the court without any pre-match practice, but showed no ill effects.
Swiatek was able to finish off victory efficiently after struggling through three sets in the previous round to defeat Varvara Gracheva despite wasting a handful of match points.
The seed claimed her 29th season victory at the Masters level and will be competing in her 18th quarterfinal in the elite series.
Swiatek secured the opening set in 31 minutes and was untroubled as she rolled through the second.
"It was a bit windy and conditions were tough," Swiatek said. "I tried to focus on easy things, like keeping the ball.
"It was not easy to win without a warmup, but I'm glad I was able to go out and play great tennis anyway."
Sixth seed Jessica Pegula won a delayed second-round match over 2023 runner-up Karolina Muchova 5-7, 6-4, 6-2.
Mother-of-two Caroline Wozniacki continued her WTA comeback effort but lost to Anastasia Pavlyuchenkova 7-5, 6-4.
Olympic champion Zheng Qinwen beat Poland's Magdalena Frech 6-1, 7-5.