Top seeds Novak Djokovic and Aryna Sabalenka have suffered an early exit from the US Open mixed doubles, falling 1-4, 4-2, 10-2 to Henry Patten and Katerina Siniakova in their opening match.
Djokovic, a 24-time grand slam singles champion, and four-time major winner Sabalenka made a strong start by taking the opening set.
However, Patten and doubles specialist Siniakova hit back to claim the second before dominating the tiebreak to secure a place in the quarterfinals.
Siniakova sealed the upset in style with an ace out wide on match point, ending the tournament hopes of the star-studded pairing.
"It wasn't looking very good for a while," Patten said.
"In this format we play one bad game and all of a sudden the first set's gone.
"We knew the same could happen in the second, and we played an amazing tiebreak. Kat acing Novak on match point was great."
The mixed doubles championship is once again being staged in the week before the singles main draw, after organisers revamped the format last year to attract more leading singles players by reducing the field and giving the event a standalone slot on the calendar.
The revamped format proved a commercial success in its debut year, drawing sellout crowds and attracting many of the sport's biggest singles names despite criticism from some doubles specialists, who argued it marginalised established pairings.
Italian duo Sara Errani and Andrea Vavassori went on to retain the title by defeating Iga Świątek and Casper Ruud in last year's final.
No problems for Williams and Alcaraz
Serena Williams made a triumphant return to the US Open, partnering with Carlos Alcaraz to beat Erin Routliffe and Lloyd Glasspool 5-3, 4-1 in the opening round.
The 23-time major winner had not competed at Arthur Ashe Stadium since her tearful farewell from the sport in 2022.
The crown jewel of American tennis erupted in deafening cheers as their queen took the court again.
The 44-year-old Williams had an easy rapport with Alcaraz, who is 21 years her junior, as the partners grinned and giggled their way into the quarterfinals, where they will meet Belinda Bencic and Flavio Cobolli later on Tuesday.
"It's always such an amazing place to be here," Williams said. "I never expected to be back on this court."
Williams hit a backhand winner the first time she touched the ball, earning uproarious cheers from the packed house a little more than two months after she announced her stunning comeback.
After trading breaks, Williams blasted a 193.1kmh ace on the penultimate point in the seventh game, drawing audible gasps from the crowd. Alcaraz, who has not played since April due to injury, shook off the early rust to close out the set with a forehand winner.
They sprinted through the second set with ease, embracing after the win in their matching royal purple outfits.
"I'm playing next to the one and only Serena Williams," seven-times major winner Alcaraz said. "Trying to do the things she told me to do."
