Top seed Ekaterina Makarova beat Alison Van Uytvanck 7-5, 7-5 to progress to the second round of the Citi Open on Tuesday.
Makarova raced out to a 2-0 lead in the first set before Van Uytvanck won the next four games to make it 4-2 in her favour. However, Van Uytvanck was unable to keep Makarova at bay for long and the Russian went on to win five of the next six games to take the opening set 7-5.
The second set proved to be a more even affair, with neither player able to engineer a break in the opening nine games. Van Uytvanck edged ahead at 5-4 after saving two break points, but Makarova then reeled off the next three games to win the second set 7-5 and with it the match.
Second seed Samantha Stosur became the 15th active player to reach 500 WTA career wins following her comfortable 6-2, 6-2 victory over France's Kristina Mladenovic.
Third seed Belinda Bencic also triumphed in her first round match, beating Tereza Smitkova 7-5, 6-4, while fourth seed Svetlana Kuznetsova defeated Sanaz Marand 6-2, 6-4.
However, there was an upset on the day, with seventh seed Coco Vandeweghe beaten by American compatriot Christina McHale 2-6, 6-4, 4-6 in just over two hours.
The other players that advanced to the second round were Naomi Brady, Sloane Stephens and Polona Hercog.