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.