Top seed Sloane Stephens defeated Elena Vesnina in the final to win the Volvo Car Open in 2016, which is her most recent prior appearance at the event. Stephens will meet Sara Sorribes Tormo for the first time.
Defending champion Kiki Bertens claimed the title last year after beating Julia Goerges in the final. This will be her first meeting with 159th-ranked qualifier Martina Trevisan.
Andrea Petkovic is making her seventh straight appearance in Charleston. She won the title in 2014, defeating Jana Cepelova in the final, and also reached the 2015 semifinals before falling to her compatriot Angelique Kerber. Petkovic has a 12-4 win-loss record at the tournament overall.
Petkovic, however, has lost both of her prior meetings with Varvara Lepchenko, both of which came on clay. They will have a rematch of their first-round encounter from this very event last year, which Lepchenko won 6-4, 7-5.
The other former champions who are in the main draw are 2009 titlist Sabine Lisicki, who lost in the first round on Monday, and 2011 champion Caroline Wozniacki, who will play her second-round match (after a first-round bye) later in the week.
In an all-American affair, Madison Brengle takes a 2-0 head-to-head lead into her match with Danielle Collins. One of those wins came in the final of a clay-court Challenger event which also took place in Charleston, in 2017.