Dutch fifth seed Kiki Bertens was dumped out of the French Open on Sunday when Italian qualifier Martina Trevisan registered a surprise 6-4, 6-4 victory to advance to the quarter-finals.
The 26-year-old Trevisan, ranked 159, had not won a Grand Slam main draw match before this tournament.
She goes on to face Polish teenager Iga Swiatek, who knocked out top seed Simona Halep, for a place in the last four.
"I'm living in a dream," said Trevisan, who saved two match points against Maria Sakkari in the third round.
"I came here two weeks ago to play my qualifying but today I'm here in the quarter-finals.
"Oh my god, I can't believe it. I'm really honoured to play on this court with Bertens who for me is an incredible player."
Trevisan raced into a 5-1 lead in the opening set but dropped serve twice before breaking Bertens for a third time in a lengthy 10th game.
The Italian surged 3-0 ahead in the second set but 2016 semi-finalist Bertens again rallied by winning the next three games.
Trevisan steadied herself and regained the initiative, failing to serve out the match at 5-3 but wrapping up the biggest win of her career in the following game.
Once a promising junior player, reaching the semi-finals in the girls doubles at Roland Garros and Wimbledon over a decade ago, Trevisan's only other appearance in the main draw of a major came at the Australian Open in January.
She recently opened up on her struggles with anorexia which prompted her to spend four years away from tennis.