Naomi Osaka battled into the last 16 of the Qatar Open on Tuesday but Coco Gauff and Ons Jabeur crashed to surprise second-round exits with straight-sets defeats.
Four-time Grand Slam champion Osaka brushed past Croatia's Petra Martic 6-3, 7-6 (11/9), continuing a comeback from maternity leave after giving birth to her daughter in July.
Osaka grasped control with a break in the fourth game of the opening set. She broke twice more in the second set -- either side of dropping her own serve -- only to blow a chance to close out the match at 5-4.
Martic threatened to force a third set as she won the first four points of the tie-break, but Osaka then saved four set points before her opponent double-faulted down match point.
It is the first WTA tournament in almost two years at which Osaka has won back-to-back matches. She goes on to play Ukraine's Lesia Tsurenko, who knocked out fourth seed Jabeur 6-3, 6-2.
Tsurenko won nine straight games from 3-1 down in the first set to notch her first victory over a top-10 player in five years.
Jabeur has endured a difficult start to the year. She admitted she was still hampered by a right knee problem that affected her in Abu Dhabi.
"Definitely much better than last week, but it's still there, unfortunately," said Jabeur.
"It will not heal in two or three days, but I'm doing my best to heal it, and I think it's going to be very positive for the next weeks."
World number three Gauff lost 6-2, 6-4 to Katerina Siniakova in her opening match, marking the first time she has failed to reach the quarter-finals of a tournament since Wimbledon last year.
US Open champion Gauff dropped serve six times in an error-strewn display, blowing a 4-0 lead in the second set.
Siniakova will face Danielle Collins in the last 16.
Elena Rybakina, seeded third, raced past China's Zhu Lin 6-2, 6-1. She meet American Emma Navarro for a place in the quarter-finals.
Earlier on Tuesday, Australian Open runner-up Zheng Qinwen battled to victory in her first match since losing the Melbourne final to Aryna Sabalenka, beating Magda Linette 6-2, 2-6, 6-3.