Top seed Aryna Sabalenka and defending champion Garbine Muguruza came through their first-round matches unscathed at the Dubai Tennis Championships on Tuesday.

Belarusian Sabalenka made light work of 19-year-old Marta Kostyuk, sealing a 6-4 6-1 win in one hour and 15 minutes.

Standing in her way of a third consecutive quarter-final in Dubai is Petra Kvitova, who beat Camila Giorgi on Monday.

Last year's champion and fourth seed Muguruza began her title defence with a 7-6 (7-5) 2-6 6-2 win over Czech qualifier Katerina Siniakova in two hours and 24 minutes.

Spaniard Muguruza will face Veronika Kudermetova in the second round after the Russian beat former world number one Victoria Azarenka in straight sets earlier on Tuesday.

There were also wins for eighth seed Ons Jabeur and 10th seed Elina Svitolina against Vera Zvonareva and Mayar Sherif respectively.

Elsewhere, there was a shock as qualifier Elena-Gabriela Ruse dumped out third seed Paula Badosa 6-3 5-7 6-4.

Ninth seed Danielle Collins is also out after the American retired due to dizziness in the second set against Marketa Vondrousova.

Sofia Kenin failed to put up a fight as she went down 6-1 6-2 to Jelena Ostapenko.