Serena Williams will face sister Venus in the Top Seed Open second round after contrasting wins on Tuesday.
In action for the first time since the WTA Tour season was suspended in March due to the coronavirus pandemic, Serena edged past Bernarda Pera.
The top seed at the WTA International event, Serena recorded a 4-6 6-4 6-1 victory after being five points from defeat.
The 23-time grand slam champion raced through the final set, losing just seven points on serve to advance in Lexington.
Awaiting Serena in the second round is Venus, who was too good for Victoria Azarenka 6-3 6-2.
The sisters will meet for the 31st time, with Serena holding an 18-12 win-loss record over Venus.
Sloane Stephens had endured a tough start to 2020 before the season was suspended, and the 2017 US Open champion suffered another loss.
The seventh seed was well beaten by qualifier Leylah Fernandez 6-3 6-3 to slip to a 1-6 win-loss record this year.
The only other seed in action was Yulia Putintseva, who brushed past Ajla Tomljanovic 6-0 6-4.
Coco Gauff, 16, was pushed in her opener, overcoming Caroline Dolehide 7-5 7-5.
CiCi Bellis, Shelby Rogers, Jil Teichmann, Anna Blinkova and Olga Govortsova also advanced.