World No 4 Elina Svitolina blamed a hip injury for her humiliation at the hands of Australian Open debutant Elise Mertens on Tuesday.
The fourth seed from Ukraine had her nine-match win streak shattered in the quarterfinal 6-4, 6-0 by unseeded Belgian Mertens on Rod Laver Arena.
"Today was very tough for me physically," said Svitolina, who was attempting to reach her first Grand Slam semifinal.
"Going into the tournament, I had a few issues with my health. Yeah, it was very sad that today I was not feeling great."
The in-form Ukrainian, who won more WTA events than any other player in 2017, said she had suffered the injury in winning the Brisbane International earlier this month.
"It was my hip. I started to feel it actually after the final in Brisbane," she said.
"Then it was getting worse and then was up and down. You know, I always had the tape, like, a heavy tape under the shorts.
"It's been there all the time. I had pain all the time. But with painkillers, it was fine."
World number 37 Mertens, on a 10-match unbeaten streak after winning in Hobart this month, sent Svitolina packing in just an 1hr 13min to become the first Belgian to make the last four since Kim Clijsters in 2012.
"You know, she played great tennis. Long rallies," said Svitolina. "I couldn't push on the serve. I gave her this chance to play well, and she did it.
"She didn't give me opportunities. All the credit to her, because she played really good tennis. I couldn't really match it."
Svitolina had needed a run to the final to have a chance of displacing Simona Halep at the top of the world rankings.
In her 22nd Grand Slam appearance, the Ukrainian has now been thwarted three times at the quarterfinal stage, the other two occasions being at Roland Garros in 2015 and last year.