Russian qualifier and world No 292 Anastasia Gasanova sent former top-ranked Karolina Pliskova crashing out of the season-opening Abu Dhabi WTA event on Saturday in a straight sets triumph.
The 21-year-old Gasanova won 6-2, 6-4 to reach the round of 16 and record her first ever victory over a player in the top 100.
Gasanova, making her main draw debut, needed just 73 minutes to see off the third seed.
"I'm really surprised, but when I woke up today, I thought, 'Why not? Why can't I win this match?'," said Gasanova.
"Actually, I had thought I would lose in qualies or something like that, but I just kept pushing myself, like, I need to win and I want to win."
Gasanova goes on to face Spain's Sara Sorribes Tormo for a place in the quarter-finals.
Ukrainian second seed Elina Svitolina eased past Russian veteran and two-time Grand Slam runner-up Vera Zvonareva 6-4, 6-1.
Greece's Maria Sakkari, seeded nine, defeated US teenager Coco Gauff 7-5, 6-2.
Results from the WTA Abu Dhabi tournament on Saturday (x denotes seeded player):
Maria Sakkari (GRE x9) bt Coco Gauff (USA) 7-5, 6-2
Garbine Muguruza (ESP x5) bt Aliaksandra Sasnovich (BLR) 6-1, 6-4
Darya Kasatkina (RUS) bt Karolina Muchova (CZE x12) - walkover
Elena Rybakina (KAZ x6) bt Wang Xiyu (CHN) 6-4, 6-4
Marta Kostyuk (UKR) bt Hsieh Su-Wei (TPE) 6-3, 6-7 (4/7), 6-3
Anastasia Gasanova (RUS) bt Karolina Pliskova (CZE x3) 6-2, 6-4
Ekaterina Alexandrova (RUS x17) bt Heather Watson (GBR) 7-5, 6-7 (7/9), 6-3
Elina Svitolina (UKR x2) bt Vera Zvonareva (RUS) 6-4, 6-1