The 26-year-old Spaniard let slip a 5-1 second set lead as her American opponent stormed back to win 6-2, 7-5 to reach her first Grand Slam semi-final.
"I was a complete disaster. I never had the momentum in this match. It was 5-1, but I never felt myself in the court," said Badosa, playing in her first quarter-final in the city where she was born.
"I didn't feel well serving or playing well from the baseline. That's my biggest strength. So I think today it surprised me."
She added: "I think losing a set from 5-1 up, I never did that before. There is always a first time for something, so it had to come today unfortunately. I lost 20 points almost in a row. It's very weird."
Badosa said, however, she will take some comfort from her rollercoaster summer.
Three months ago, she was on the brink of retiring due to a persistent back injury which forced her to quit a number of matches and saw her ranking tumble outside of the top 100.
However, she clinched the Washington hard court title and arrived at the US Open with her world ranking restored to the top 30.
"When I started in Washington I would sign for all the results," she said.
"But now I have to wait four months for the next Slam, so that sucks. When you feel so bad with such negative thoughts, you want to leave because in the end you become an ant."
