Ons Jabeur, a semifinalist last week in Indian Wells, Calif., was forced to retire from her first-round match Tuesday in the VTB Kremlin Cup in Moscow due to a right elbow injury.
The fifth-seeded Tunisian was trailing Russia's Ekaterina Alexandrova 6-1, 1-0 when she halted the match. Jabeur had just risen to a career-high ranking of No. 8 in the world this week, the top rating ever for an Arab player.
Elsewhere in the first round, the Czech Republic's Marketa Vondrousova upset seventh-seeded Elena Rybakina of Kazakhstan 6-4, 6-4. Eighth-seeded Simona Halep of Romania rolled past Russia's Anastasia Potapova 6-1, 6-4, and ninth-seeded Anett Kontaveit of Estonia topped the Czech Republic's Katerina Siniakova 6-3, 6-3.
The Czech Republic's Tereza Martincova and Germany's Andrea Petkovic also advanced.
Tenerife Ladies Open
Third-seeded Sara Sorribes Tormo squandered a 5-1, third-set lead and lost 6-4, 5-7, 7-6 (4) to Russia's Varvara Gracheva in the first round in Tenerife, Spain.
Gracheva won five consecutive games to get back into the match, dropping just five points in that span.
Fifth-seeded Viktorija Golubic of Switzerland also dropped her opening match, falling 6-3, 6-4 to the Netherlands' Arantxa Rus. Croatia's Donna Vekic defeated eighth-seeded American Alison Riske 6-1, 6-4.
Other first-round winners were fourth-seeded Camila Giorgi of Italy, seventh-seeded Clara Tauson of Denmark, France's Alize Cornet, Egypt's Mayar Sherif, China's Saisai Zheng, Montenegro's Danka Kovinic and Belgium's Greet Minnen.
--Field Level Media