Top seed Simona Halep eased into the Qatar Open quarterfinal with a 6-2, 6-3 victory over Ukrainian Lesia Tsurenko on Wednesday.
Fresh from helping Romania reach their first Fed Cup semifinal, Halep made a blistering start by racing into a 5-0 lead in the opening set.
She held off a brief challenge from Tsurenko in the second set before reeling off the last five games of the match to improve her head-to-head record against her opponent to 6-0.
Ninth seed Julia Goerges battled past American lucky loser Alison Riske 6-1, 6-7 (5), 6-4 in a marathon encounter, recovering from 2-4 down in the final set.
Fourth seed Elina Svitolina began her campaign with a 6-4, 6-4 win over 2017 French Open champion Jelena Ostapenko, avenging her two previous losses to the Latvian.
A neck injury has hampered the Ukrainian, who was playing her first match since the Australian Open quarterfinal defeat by eventual champion Naomi Osaka of Japan in January.
"I have been struggling since the Australian Open with my neck," Svitolina said after the match.
"It depends... on the practice, on the match, what I have, so it's tough to tell how I'm going to feel tomorrow, but every single day I try to get a treatment, I try to get some work done, and, you know, it's just a process."
Swiss wildcard Stan Wawrinka booked a quarterfinal place at the ABN AMRO World Tennis Tournament in Rotterdam with a 6-4, 7-6 (4) victory over Canadian fourth seed Milos Raonic on Wednesday.
Wawrinka, seeking his first title since undergoing knee surgery in 2017, will next face another Canadian for a place in the last four after Denis Shapovalov defeated Tomas Berdych 6-4, 6-3 at the Ahoy arena.
Earlier on Wednesday, Damir Dzumhur outwitted third seed Stefanos Tsitsipas 6-4, 1-6, 7-5 in an opening round match.
Isner pips Tomic
John Isner made quick work of Australia's Bernard Tomic to advance to the quarterfinal of the New York Open on Wednesday with a 7-6 (7), 6-4 victory.
The big-serving American sent down 27 aces, won 85 per cent points on his first serve and did not face a single break point as he wrapped up the match in 74 minutes at the Nassau Veterans Memorial Coliseum.
In the quarterfinal, the American will face Australian seventh seed Jordan Thompson, who defeated Christopher Eubanks 4-6, 6-1, 6-4 earlier on Wednesday.
Spain's Jaume Munar battled back from a set down to defeat second-seeded Italian Fabio Fognini 4-6, 6-4, 7-5 in the Argentina Open on Wednesday and advance to the quarterfinals.
He will battle local hope Guido Pella for a place in the semifinals.