Naomi Osaka's hopes of a third US Open title were dashed in the first round Tuesday as the Japanese star slumped to a straight sets loss against Danielle Collins.
Four-time Grand Slam champion Osaka, a winner at Flushing Meadows in 2018 and 2020, was beaten 7-6 (7/5), 6-3 by 19th-seeded American Collins in a battle of two big hitters.
Collins, finalist at this year's Australian Open, now advances to a second round clash with Spain's Cristina Bucsa.
The 28-year-old right-hander from Florida will head into that assignment brimming with confidence after showing great composure to put away Osaka on Arthur Ashe Stadium.
No one was more surprised at the victory than Collins, who had skipped tournaments in Silicon Valley and Toronto to allow herself time to recuperate from a neck injury.
"I'm just really still kind of speechless in a way because I took the summer off," Collins said. "To kind of come out here, play a tough opponent first round, someone that's won two Grand Slams here, it's not easy.
"Just really over the moon about being able to get through this first round because I don't think most players want to face Naomi in the first round."
Former world number one Osaka, whose ranking has fallen to 44 after an inconsistent year, made a smooth start with an early break to take a 3-0 lead.
But Collins battled back into the match and took the first set after winning a hard-fought tie-break.
With both players producing some booming groundstrokes, the second set was a question of who would blink first.
Collins put herself on the threshold of victory after breaking Osaka for a 5-3 lead in the eighth game.
Osaka, 24, came within touching distance of securing the break of serve needed to keep the match alive after taking a 15-40 lead in the ninth game.
But Collins rallied back to deuce and then seized victory on her first match point when Osaka hit a return long.
Osaka later said she had been bothered by a niggling back problem.
"I tried as hard as I could. I wanted to play without my back being in pain. I only really started serving two days ago," she said.