Simona Halep has started her campaign at the WTA Tour's Kremlin Cup with a straight-sets win but Ons Jabeur retired from her first-round match.

Halep cruised past Anastasia Potapova 6-1 6-4, despite dropping her serve three times.

The Romanian eighth seed will play Veronika Kudermetova in the second round after the Russian beat 18-year-old qualifier Oksana Selekhmetova 4-6 7-6 (7-3) 6-4.

Halep hasn't won more than three consecutive matches since returning in August from a three-month layoff with a calf injury that kept her out of the French Open and Wimbledon.

Eighth-ranked Jabeur retired when 6-1 1-0 down against Ekaterina Alexandrova.

There was no immediate information from the Tunisian or the WTA about the reason for her retirement, which makes it harder for Jabeur to qualify for the season-ending WTA Finals.

Marketa Vondrousova eliminated seventh-seeded Elena Rybakina 6-4 6-4 to set up a meeting with qualifier Lesia Tsurenko in the next round.

Anett Kontaveit eased to a 6-3 6-3 win over Katerina Siniakova to advance to a second-round match with experienced German Andrea Petkovic, who was leading 2-6 6-0 2-0 when her opponent Jelena Ostapenko retired.