Seven-time major winner Alcaraz was playing his first competitive match since April after injuring his wrist, while 23-time Grand Slam champion Williams was competing in New York for the first time since she “evolved away” from tennis in 2022.
The pair were greeted by huge cheers and were roared on throughout their opening 5-3 4-1 win against Great Britain’s Lloyd Glasspool and New Zealand’s Erin Routliffe.
The 44-year-old Williams won the US Open mixed doubles title in its original format alongside Max Mirnyi in 1998 – five years before Alcaraz was born.
Almost 30 years later, Williams still had the competitive desire. She and Alcaraz enjoyed the occasion, playing with smiles on their faces and roaring each other on after winning a point.
Interviewed during a change of ends, Alcaraz said: “I’m playing next to the one and only Serena Williams, so what else can I do? Just enjoy and try to do the things she told me to do.”
Their partnership improved rapidly in their first match as they won eight of the final nine games to seal victory.
However, they were denied a place in Wednesday’s semi-finals by Italy’s world number six Flavio Cobolli and Swiss team-mate Belinda Bencic, who won 5-4 (7-4) 4-1.