NEW YORK - Two-time champion Naomi Osaka's return to the US Open ended in the second round on Thursday with a 6-3, 7-6 (7/5) loss to 52nd-ranked Czech Karolina Muchova.
Japan's Osaka, who won the title in 2018 and 2020, missed last year's edition after the birth of her daughter Shai. She hasn't reached the third round of a Grand Slam since the 2022 Australian Open.
She has been unable to build momentum in her comeback and her first round win over Jelena Ostapenko was her first in four years over a top-10 player.
Muchova was another tough opponent. A semi-finalist at New York last year, she reached a high of eighth in the world before she missed nine months after undergoing wrist surgery.
"Honestly, this year the biggest win for me is that I could play again," said Muchova, who had played just a dozen matches since returning at Eastbourne in June.
"I'm really grateful I'm able to play tennis and that I made it here. This is just the cherry on top to be here in this stadium. It's crazy."
Osaka returned to the Arthur Ashe Stadium where she captured her first Grand Slam title with an upset of Serena Williams in 2018 in style -- stepping on court in a made-for-the-lights black version of her custom Nike US Open kit.
She made a confident start, but she couldn't convert an early break point and there were too many miscues in the face of devastating pressure from Muchova at the net.
The Czech broke for a 4-3 lead in the first as she put together a run of five straight games.
Osaka stopped the rot with a steely hold for 1-1 in the second set and broke Muchova for a 5-4 lead in the second.
But she wasted three set points in the next game as Muchova regained the break, leveling the set when Osaka smashed a forehand long.
Osaka had a 4-2 lead in the tiebreaker when her fourth double fault opened the door. Muchova won four straight points to give herself a pair of match points, Osaka saving one before she banged another wild forehand long.