Ashley Harkleroad was forced to retire from her first-round clash at the Nasdaq-100 Open in Miami on Wednesday because of a blister on her hand.
The 19-year-old American was trailing 6-2 3-0 against compatriot Jill Craybas when she withdrew.
Czech Klara Koukalova beat Alexandra Stevenson of the USA 5-7 7-5 6-0, and goes on to meet Jennifer Capriati.
Top seed Serena Williams makes her long-awaited return to action against Spain's Marta Marrero on Friday.
French prodigy Tatiana Golovin eased past Anabel Medina Garrigues of Spain 6-1 6-3, and will face 23rd seed Dinara Safina in round two.