An emotional Emma Raducanu said she should have got more matches under her belt ahead of the US Open after the former champion lost 6-1 3-6 6-4 in the first round to American Sofia Kenin on Tuesday.
Kenin, the 2020 Australian Open winner, put on an aggressive display with six aces and 45 winners to set up a meeting with compatriot Jessica Pegula in the next round.
Britain's Raducanu has struggled to recapture the magic of her fairytale run through New York three years ago when she became the first qualifier to win a Grand Slam.
She skipped key tune-up events in Toronto and Cincinnati, taking a different approach in her buildup to the year's final major, but struggled to find her feet as Kenin ripped through the opening set.
"I would have probably preferred to play a little bit more," Raducanu said. "When I have a lot of matches, just like every player, you feel really good, you feel like everything's automatic. So yeah, I think I can learn from it."
Raducanu, who raised hopes of a renaissance when she reached the fourth round at Wimbledon this year, upped her level in the second set and got the critical break in the fifth game.
She broke the American again with a forehand winner to close out the set but then ran out of steam, dropping serve with a double fault in the fifth game of the decider before Kenin went on to seal victory with a hold to love in the final game.
"It was a very tough match -- Emma's a previous champion here so of course I kind of felt that," Kenin said.
"I felt like I had to dig deep to get the win."
Raducanu has not won a match at Flushing Meadows since picking up her lone major title. She was knocked out in the first round in 2022 and missed the tournament a year later due to injury.
She became emotional briefly during a post-match news conference but said she would try to take away some positives from her latest major campaign.
"I feel down. I feel sad," she said. "Obviously this is a tournament that I really want to do well in."