Djokovic, a 24-time Grand Slam singles champion, and four-time major winner Sabalenka made a strong start by taking the opening set. But Patten and doubles specialist Siniakova hit back to claim the second before dominating the tiebreak to secure a place in the quarter-finals.
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, in this format we play one bad game and all of a sudden the first set's gone," Patten said.
"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 Swiatek and Casper Ruud in last year's final.
US Open 2026
The US Open is the fourth and final Grand Slam of the tennis season, running from August 30th to September 13th. It is a hard-court tournament held at Flushing Meadows in New York City. Follow the links below for more information!
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