Belinda Bencic survived a scare as she advanced to the Charleston Open second round with a 4-6 7-6 (7-5) 6-3 win over Wang Xiyu.
The Olympic gold medallist was a semi-finalist in Miami last time out, while she has also reached the quarter-finals in Sydney and St Petersburg this year.
However, the 10th seed was in danger of falling at the first hurdle at 5-2 down in the second set against world number 149 Wang.
Bencic rallied to force a tie-break and, subsequently, a deciding set, which she controlled to set up a second-round clash with 16-year-old Linda Fruhvirtova.
Magda Linette also fought back from the brink of defeat; the world number 64 saving a match point before prevailing against Maria Voleynets 4-6 6-3 7-6 (7-4).
Although, there was no joy for former champion Sloane Stephens, who was beaten in three sets by Zheng Qinwen.
Stephens – winner here in 2016 – recovered from losing the opening set 6-3 to take the second 6-4. But there was no denying the Chinese teenager, who dropped just nine points as she raced through the decider 6-0 to claim the first top-50 win of her career.
The likes of Jessica Pegula and Madison Keys were due to feature in the evening session, which was postponed due to severe inclement weather including the possible threat of a tornado.
In Bogota, top seed and home favourite Camila Osorio advanced to the last 16, but only after opponent Ylena In-Albon was forced to retire at 2-2 in the deciding set.
Fourth seed Hanna Udvardy and eighth seed Harriet Dart were beaten in straight sets by Dayana Yastremska and Elina Avanesyan respectively.