Top seed Simona Halep eased into the Qatar Open quarter-finals with a 6-2, 6-3 victory over Ukrainian Lesia Tsurenko on Wednesday.
Fresh from helping Romania reach their first Fed Cup semi-final, 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.
World number three Halep, who received a bye in the opening round, will next face ninth seed Julia Goerges.
The German battled past American lucky loser Alison Riske 6-1, 6-7(5), 6-4 in a marathon encounter, recovering from 4-2 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 quarter-final 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."
There were moments in the match when Ostapenko was unplayable as she unleashed aggressive forehands from the baseline to recover from early breaks of serve in both sets.
But Svitolina maintained her service rhythm to ensure she controlled the match in the critical moments and went on to convert five break points en route a convincing victory.
"The ball is flying and the wind is very tricky, so I had to be extremely quick with my feet. In the end I was very pleased that I could finish in two sets," added Svitolina, who will meet Czech qualifier Karolina Muchova in the quarter-finals.
Earlier on Wednesday, Czech Karolina Pliskova was forced to withdraw from the tournament due to a viral illness.
The 2017 Doha champion is the fifth withdrawal since the draw was made following Danish sixth seed Caroline Wozniacki (viral illness) and France's Caroline Garcia (leg injury).
Sharapova pulls out of Indian Wells with shoulder injury
Former World No 1 Maria Sharapova will miss next month's BNP Paribas Open at Indian Wells due to a right shoulder injury, organisers said on Wednesday.
The shoulder problem had also forced the 31-year-old to withdraw from her second-round match in St Petersburg, Russia last month.
"We will miss Maria this year and hope to see her back at Indian Wells next year!" the tournament said on Twitter.
Sharapova's withdrawal allowed German Mona Barthel to secure a spot in the Indian Wells singles draw. The tournament will take place from March 4-17.
Youngster Munar ousts Italy's Fognini in Argentina
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 quarter-finals.
The unseeded 21-year-old, who qualified for last month's Australian Open but retired against Fognini in his first match, followed up his run to last year's ATP Next Gen semi-finals by beating the World No 15 at the second time of asking.
"It's the best victory of my career," said Munar, who is ranked 77th in the world.
Fognini had Munar on the ropes in the final set and got to within two points of victory, but the youngster rallied, breaking the 31-year-old to level at 5-5 and winning with a burst of 12 points in a row.
He will battle local hope Guido Pella for a place in the semi-finals.
Wawrinka powers into Rotterdam quarter-finals
Swiss wildcard Stan Wawrinka booked a quarter-final place at the ABN AMRO World Tennis Tournament 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 in Rotterdam.
"Tonight was a really good level, that is for sure," Wawrinka told reporters.
"It is one of the best matches I have played in many months now. So far I have (played) two great matches (in Rotterdam), tonight was a great performance."
Three-time Grand Slam winner Wawrinka was delighted with his workout as he had been beaten by Raonic in their last three meetings.
"I was feeling great physically, so that is how I can start to engage the rally. I was returning better because I reacted better and that gave me way more chances to be aggressive.”
Earlier on Wednesday, Damir Dzumhur notched up his first victory of 2019 when he outwitted third seed Stefanos Tsitsipas 6-4, 1-6, 7-5 in an opening round match.
Isner defeats Tomic to advance to New York Open quarters
John Isner made quick work of Australia's Bernard Tomic to advance to the quarter-finals 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 percent 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.
"I definitely served very well," Isner said after the match.
"I was down a set point in the first set and I came up with three aces.
"I'm happy to be in the quarter-finals. Last year I lost my first match here, hopefully I continue to improve."
Isner, who was knocked out in the first round of last month's Australian Open, is the tournament's top seed after South African Kevin Anderson withdrew with an elbow injury.
Both players held firm on serve in the first set to force a tiebreak, which the 33-year-old Isner held his nerve to win.
Tomic fought till the end, striking 13 aces and saving five of the six break points he faced, as well as six match points in the second set, before Isner eventually claimed his first victory of 2019.
In the quarter-finals, the American will face Australian seventh seed Jordan Thompson, who defeated Christopher Eubanks 4-6 6-1 6-4 earlier on Wednesday.