Defending champion Petra Kvitova and former world number one Victoria Azarenka were both forced to withdraw from the WTA Qatar Ladies Open through injury on a day where the top seeds all cruised through in Doha.

Kvitova – who won the 2018 and 2021 editions of the tournament, beating Garbine Muguruza in the final on both occasions – was left unable to continue during her clash with Elise Mertens, later tweeting that an injury to her left wrist had flared up during the second set.

Her conqueror Mertens will face fourth seed and WTA St Petersburg champion Anett Kontaveit in the round of 16 after the Estonian's win over Ana Konjuh on Monday.

Meanwhile, Azarenka joined Kvitova in announcing her withdrawal through injury, suffering pain in her left hip ahead of her scheduled clash with American Madison Brengle.

The tournament's top seeds had more luck on a day of few surprises. World number two Aryna Sabalenka breezed to a 6-2 6-2 victory over France's Alize Cornet, with the Belarusian the favourite for the first WTA 1000 event of the year as world number one Ashleigh Barty is missing through injury.

Elsewhere, world number three Barbora Krejcikova made light work of Poland's Magda Linette, winning 6-1 6-3, and will face former French Open champion Jelena Ostapenko in the round of 16, having eliminated the Latvian from last month's Australian Open.

Paula Badosa also recorded a straight-sets victory, seeing off Clara Tauson 6-1 6-2 to reach the last 16, where she will face 17-year-old American Cori Gauff, who defeated France's Caroline Garcia 6-2 7-6 (7-3).

There were also three-set wins for top-10 players Iga Swiatek and Ons Jabeur, with Swiatek beating Viktorija Golubic 6-2 3-6 6-2, and Jabeur overcoming Aliaksandra Sasnovich 1-6 7-5 6-3.

In the final match of the day, world number six Maria Sakkari downed American Ann Li 6-3 6-3.