Serena Williams survived a major scare to move to within two wins of tying Steffi Graf's Open era record of 22 grand slam singles titles.
Williams headed into the quarter-finals as a huge favourite to successfully defend her title but was panicky throughout the first two sets against 60th-ranked Yulia Putintseva and was lucky to escape with a 5-7 6-4 6-1 victory.
Williams had won considerably more matches at grand slams than all of her fellow quarter-finalists put together.
Putintseva, 21, was making her first appearance in the last eight at a slam but it was Williams who looked nervous.
The Kazakh saw an early break snuffed out but did not let that worry her and broke again for 6-5 before serving out the set to love.
A feisty character, she whipped up the crowd on Court Philippe Chatrier, who were huddled under blankets in the unseasonably cold and damp conditions.
It was the first set Williams has lost on clay this year and the first time Putintseva has won a set against her.
The top seed looked to have put the danger behind her when she won four of the opening five games in the second set but back came Putintseva.
Williams could not get her feet moving in the heavy clay, although the culprit appeared more her head than the conditions.
Having seen her calendar Grand Slam hopes ended by Roberta Vinci at the US Open last year, Williams then allowed the occasion to get the better of her in the Australian Open final against Angelique Kerber in January.
When Putintseva twice forced break point at 4-4, Williams was staring at her worst slam loss since she was beaten by Virginie Razzano in the first round here four years ago.
That was the catalyst for her to hire coach Patrick Mouratoglou, since when she has won eight slam titles.
Williams must have been a relieved woman when she sat down on her chair having finally held for 5-4, and it proved to be the end of Putintseva's hopes.
The 21-year-old, who stands only 5ft 4in, double-faulted to lose the second set and, with Williams now calmer if still a bit leaden-footed, did not win another game until it was too late.
In the last four, Williams will play another unseeded player in Dutchwoman Kiki Bertens, who continued her remarkable run by upsetting eighth seed Timea Bacsinszky 7-5 6-2.
Bertens has now won 12 straight singles matches having won the title in Nuremberg the week before the French Open as a qualifier.
Ranked 89 prior to her run of success, Bertens will be seeded at Wimbledon and could yet cause more of a stir in Paris.