Chinese second seed Li Na admitted she wasn't ready mentally after crashing out in the French Open first round at the hands of world number 103 Kristina Mladenovic of France.
Following men's third seed Stan Wawrinka's exit on Monday, fellow Australian Open champion Li became the biggest early victim in the women's draw as 21-year-old Mladenovic stormed through 7-5, 3-6, 6-1 on a windswept Suzanne Lenglen court.
"Nobody says if you're number two in the world you have to win all the matches. I mean, this is tennis," said Li, the 2011 Roland Garros champion.
"I think it doesn't matter who plays today against me, I always lose because I don't think I put pressure on her," she said about Mladenovic, who reaches the last 64 for just the second time in six appearances in Paris.
Li came into the tournament in good form having reached the quarter-finals at Rome and Madrid as well as the Miami Masters final where she lost to Serena Williams.
However, her results in Paris since becoming the first Asian player to win a Grand Slam three years ago have been disappointing.
She was knocked out in the second round last year and hasn't been past the fourth round in any of her seven other appearances in the French capital.
"I think today I gave away the match," said the dejected 32-year-old double Grand Slam winner.
"I think today is not about tennis, so many things are wrong."
On Tuesday, she committed 37 unforced errors. "I don't think I'm doing well. If I'm doing well, I believe I still can win the match if it's not my best day.
"But I don't think today I tried a lot. Like I said before, doesn't matter who plays today against me. I already lose the match already."
Mladenovic next meets Alison Riske of the United States. "It's just incredible, I don't have the words to describe what happened," a tearful Mladenovic said.
"To beat the world number two in the first round at Roland Garros is incredible. Without you, I couldn't have done it," the 2009 French Open junior champion told the crowd.
The 21-year-old dug deep to steal the first set from under Li's nose when she saved two set points at 5-4 before going on to close out the opening frame 7-5.
The second set was a different story as the 32-year-old from Wuhan picked up an early break to race into a 3-0 lead which she protected the rest of the way to level the match 6-3.
Then came the Li collapse.
Mladenovic, who teamed up with Canadian Daniel Nestor to win the Wimbledon (2013) and Australian (2014) mixed doubles titles, drew first blood in the final set when she broke in the fourth game to jump into a 4-1 lead.
The match was slipping away from the Australian Open champion while Mladenovic grew in confidence knowing victory was within her grasp.
The world number two was unable to muster a fightback as Mladenovic closed out the match 6-1 for her greatest win.