Serena Williams vowed to "work five times as hard to make sure I never lose again" after crashing out in the second round of the French Open.
The tournament had previously lost Australian Open champions Stan Wawrinka and Li Na but Williams' 6-2 6-2 defeat by Spain's Garbine Muguruza was on another level.
The world number one went into the tournament as a huge favourite to retain the title she won for the second time 12 months ago.
But, within an hour of her sister Venus losing to Anna Schmiedlova, Serena trudged off the court a beaten woman. The pair had been expected to meet in the third round.
The result was surprising enough but the manner of it added to the shock. The 32-year-old had never previously won fewer than five games in any grand slam match.
Meanwhile, coupled with Li's loss to Kristina Mladenovic on Tuesday, it is the first time in the Open era that the top two seeds in the women's tournament have lost before the third round at any grand slam.
Williams, who made 29 unforced errors and hit only eight winners, said: "I don't think anything worked for me today.
"It was one of those days. You can't be on every day, and, gosh, I hate to be off during a grand slam. It happens. It's not the end of the world.
"I think she played really well and she played really smart. It's great because I'm going to go home and work five times as hard to make sure I never lose again."
Although Williams beat Alize Lim comfortably enough in the first round, the signs were there that not all was well with the top seed's game.
And in cold and windy conditions on Court Suzanne Lenglen she simply never got going.
Despite her 17 grand slam singles titles and huge experience, it is not that unusual for Williams to have days where nerves get the better of her and her movement deserts her.
One of the most painful defeats of her career came in Paris two years ago when she lost to Frenchwoman Virginie Razzano in the first round.
That was the moment she turned to coach Patrick Mouratoglou and began one of the most dominant spells of her career.
She went on to win Wimbledon, the Olympics and the US Open in the summer of 2012 and will hope for a similar response this time.
She said: "I feel like I don't have to win another match, I don't have to win another tournament. Everything and every day is a bonus for me.
"Obviously I want to do the best and I want to win and I want to be the best and that's my whole goal.
"But it's great sometimes to get knocked down because you have to get back up. I love getting back up. I love the challenge."
For all her success over the past couple of years, grand slams have been where her weakness has been and she has now failed to get beyond the fourth round at three of the last four tournaments.
But, as poor as Serena was, the match was just as much about the performance of 20-year-old Muguruza.
The world number 35 struck the ball with great power and precision and was nerveless serving out the biggest victory of her life.
The pair exchanged words at the net, with Muguruza explaining: " She said that if I continue playing like this, I can win the tournament. I said, 'I will try, I will try'. "
Venus performed much better against another young gun and raced through the first set but Schmiedlova showed impressive composure to turn the match around and win 2-6 6-3 6-4 to reach the third round at a grand slam for the first time.
Had Venus and Serena played each other, it would have been their earliest ever meeting in a knockout tournament.
Venus said: "I felt like this was a match that I was most likely going to win. I don't know how Serena felt, but I'm sure she feels like that every time she goes on the court. So I think our expectation was to play in the next round."
Eugenie Bouchard also looked in trouble, down a set to big-hitting Julia Goerges, but the 18th seed recovered to win 2-6 6-2 6-1 and next meets Swede Johanna Larsson, who upset 12th seed Flavia Pennetta 5-7 6-4 6-2.
Eighth seed Angelique Kerber was a 6-2 7-5 winner over Varvara Lepchenko.