Top seed Ons Jabeur was sent crashing out of the WTA 1000 Guadalajara Open on Wednesday, losing a grueling three-hour battle to Italy's Martina Trevisan.
Tunisian star Jabeur, the losing finalist at Wimbledon for the past two years, was downed 6-7 (4/7), 7-5, 6-3 by the unseeded Trevisan, currently ranked 54th in the world.
Jabeur looked to have taken a grip on the match after taking the first set on a tie-break and then surging into a 30-0 lead as she served for the match at 5-4 in the second set.
But the world No 7 was left stunned after Trevisan battled back to break twice in quick succession to take the set and level the match.
The 29-year-old Italian, who is chasing only the second WTA title of her career this week in Mexico, then broke for a 5-3 lead in the decider before holding to clinch victory.
Trevisan will face unseeded American Caroline Dolehide in the quarterfinals. Dolehide advanced with a 6-1, 6-2 thrashing of Russian eighth seed Ekaterina Alexandrova.
In other matches on Wednesday, Sofia Kenin's impressive return to form continued as the unseeded American upset sixth seed Jelena Ostapenko to reach the last eight.
Former Australian Open champion Kenin, who last reached the quarterfinals of a WTA 1000 event in 2019, booked her place in the last eight with a 6-4, 7-5 win in 1hr 44min.
The Moscow-born Kenin, whose ranking plunged to 426th last year, will face Canada's 2021 US Open finalist Leylah Fernandez in the last eight. Fernandez defeated unseeded American Emma Navarro 6-2, 6-3 in her last 16 clash.
Third seed Caroline Garcia of France sailed into the quarterfinals with a 7-5, 6-4 victory over Hailey Baptiste of the United States. Garcia will face 10th seed Victoria Azarenka in the last eight.
Azarenka cruised into the quarterfinals with a 6-2, 6-1 defeat of seventh seed Veronika Kudermetova.
Second seed Maria Sakkari of Greece, meanwhile, romped into a quarterfinal meeting with unseeded Colombian Emiliana Arango after a 6-2, 6-2 dismissal of Italy's Camila Giorgi.