Coco Gauff suffered a surprise early exit from the Qatar Open on Tuesday with a straight-sets defeat by Ukraine's Marta Kostyuk, while Elena Rybakina eased into the last 16.
Former US Open champion Gauff blew a healthy advantage in the second set as Kostyuk sealed a 6-2, 7-5 victory and a third-round meeting with the winner of an all-Polish tie between Magda Linette and Magdalena Frech.
Gauff, playing for the first time since January 21's quarter-final loss to Paula Badosa at the Australian Open, served seven double-faults in an erratic display.
The American made a terrible start, slipping 4-1 behind after dropping her serve twice.
Gauff was broken again in the eighth game as Kostyuk secured the first set in just half an hour.
The world number three hit back with a break en route to a 4-2 lead in the second set as she started to find her rhythm.
But Kostyuk battled back, taking advantage of an error-strewn Gauff performance which ended when she served two double-faults to be broken for the fifth time.
"The double-faults made it easier for me... I'm very happy that it ended in two sets," Kostyuk told BeIN Sports.
Rybakina, who lost to eventual winner Belinda Bencic in the Abu Dhabi semi-finals last week, saw off Payton Stearns in her opening match.
The fifth seed cruised to a 6-2, 6-4 win despite a late wobble to set up a third-round tie against either Russian teenager Mirra Andreeva or Slovakia's Rebecca Sramkova.
Rybakina led 5-0 in the second set but missed three match points to take it 6-0 and then briefly fell apart as Stearns dragged the set back on serve.
The former Wimbledon champion belatedly got over the line on her fifth match point.
Jasmine Paolini, last year's French Open and Wimbledon runner-up, also made a winning start to her campaign with a 6-3, 6-4 victory against Caroline Garcia in the second round.
Czech youngster Linda Noskova earned a last-16 tie against three-time defending champion Iga Swiatek with a 6-2, 6-3 win over Kazakhstan's Yulia Putintseva.
jc/iwd
