Only two seeded players, Simona Halep and Anett Kontaveit won their first-round matches at the Kremlin Cup on Tuesday.
Retirements ruined the rest of the day’s action in Russia’s capital. In a match between two wildcard entrants, the eighth-seeded Romanian overcame Anastasia Potapova.
Halep, a previous Moscow champion in 2013, required an hour and 30 minutes to win 6-1, 6-4.
Although Halep had an easier time breaking into the match in the first set, the second set was considerably tighter, with both players trading breaks.
Halep earned her third break in the ninth game, and although facing three break-back points while serving for the match in the tenth game, she was able to avoid them all and win the match.
Halep will face another Russian, Veronika Kudermetova, in the second round.
Kudermetova advanced to the second round after defeating compatriot Oksana Selekhmetova in the first round. Kudermetova defeated Selekhmetova 4-6, 7-6(3), 6-4 in two hours and 20 minutes.
Ekaterina Alexandrova makes it to the second round
Ekaterina Alexandrova, another Russian, advanced to the second round as well.
Alexandrova, who was playing fifth-seeded Ons Jabeur, was leading the Tunisian 6-1, 1-0 when she quit with an injury to her right elbow during the match.
The next character Alexandrova will portray is Anhelina Kalinina. Meanwhile, Kontaveit began her campaign in Moscow as the ninth seed, following the withdrawal of sixth-seeded Angelique Kerber.
The Estonian required an hour and 13 minutes to beat Katerina Siniakova of the Czech Republic 6-3, 6-3. For a spot in the quarter-finals, the 20th-ranked Kontaveit will face Andrea Petkovic.
Petkovic advanced to the second round because Jelena Ostapenko, her first-round opponent, retired in the fourth set.
At the time of Ostapenko’s retirement, the German was ahead 2-6, 6-0, 2-0. Marketa Vondrousova and Tereza Martincova, both Czechs, finished second in the Kremlin Cup’s second round.
In 1 hour and 22 minutes, Vondrousova defeated seventh seed Elena Rybakina, 6-4, 6-4.
Martincova, meanwhile, was the first to win her match on Tuesday, defeating Irina Bara 6-0, 7-5.
In the second round, Vondrousova will face Lesia Tsurenko, while Martincova will face second seed, Garbine Muguruza is a tennis player from Spain.