Victoria Azarenka booked her spot in the second round of the Qatar Open with a 6-2 6-3 win over Svetlana Kuznetsova on Monday.
It was the first time the pair had faced off since the final of the 2016 Miami Open and Azarenka, who won back-to-back titles in Doha in 2012 and 2013, struck first, eventually claiming the opening set in 44 minutes.
She needed six match points to see off Kuznetsova in the second set to tee up a last-16 meeting with either Laura Siegemund or Elena Rybakina.
There was also a win for former world number one Garbine Muguruza, who defeated Veronika Kudermetova 6-2 7-6 (7-4).
"Veronika was a very tough opponent," Muguruza told a media conference. "[I'm] just happy with this win. We played a year ago, and I remember it was a tough match. I'm happy to have closed it in two sets."
Fifth seed Kiki Bertens, meanwhile, was dumped out by a rampant Jelena Ostapenko in straight sets.
The 2017 French Open champion hit 26 winners on her way to an emphatic 6-0 6-2 win against her Dutch opponent, who was playing her first match in five months following Achilles surgery.
Anett Kontaveit overcame number seven seed and beaten Australian Open finalist Jennifer Brady 6-1 6-2 to set up a second-round clash with Angelique Kerber, who beat Cagla Buyukakcay 6-4 6-2.
In the day's other match, Maria Sakkari beat Mayar Sherif 6-0 6-3.
Meanwhile, teenage qualifier Clara Tauson shocked number one seed Ekaterina Alexandrova 6-3 6-4 in the first round of the Lyon Open.
There were also wins for Arantxa Rus, Nina Stojanovic, Timea Babos, Greet Minnen and Fiona Ferro in France.