World number three Coco Gauff lost in 73 minutes to Marta Kostyuk in the second round of the Qatar Open.
The Ukrainian, the world number 21, fought back from 3-1 down in the second set to wrap up a 6-2 7-5 victory at the WTA 1,000 event in Doha.
It is a second successive defeat for Gauff, who received a bye in the first round and was playing for the first time since she lost to Paula Badosa in the quarter-finals of the Australian Open last month.
The 2023 US Open champion was undone by seven double faults and 39 unforced errors while she managed just eight winners.
Gauff had won her last 17 matches against opponents ranked outside the top 20 before facing Kostyuk.
The 22-year-old will now face the winner of an all-Polish tie between Magda Linette and Magdalena Frech.
Elsewhere, former Wimbledon champion Elena Rybakina claimed a 6-2 6-4 win against American Peyton Stearns, while Jasmine Paolini – last year’s Wimbledon and French Open runner-up – defeated Caroline Garcia 6-3 6-4.
Linda Noskova won 6-2 6-3 against Kazakhstan’s Yulia Putintseva to set up a last-16 meeting with three-time defending champion Iga Swiatek.
