The Czech Republic's Lucie Hradecka beat slumping Canadian star Eugenie Bouchard 6-4, 3-6, 6-2 on Wednesday in the first round of the Miami Open.
Bouchard entered the week ranked 45th in the world, 40 spots higher than Hradecka.
Hradecka set up a match with Belgium's Kirsten Flipkens.
American Christina McHale outlasted Japan's Doi Misaki 6-2, 4-6, 7-5, and CoCo Van DeWeghe beat Samantha Crawford 6-4, 7-5 in an all-American match.
In men's play, Canada's Vasek Popisil defeated Diego Schwartzman of Argentina 2-6, 6-3, 7-6 (4) to advance to the second second round.
American Taylor Fritz topped Italy's Simone Bolelli 6-4, 6-2; Britain's Kyle Edmund held off Jiri Vesely of the Czech Republic 6-4, 5-7, 7-6 (6); Albert Ramos-Vilonas of Spain topped Colombian qualifier Alejandro Gonzales 5-7, 6-2, 7-6 (3); and Spain's Fernando Verdasco beat Gilles Muller of Luxembourg 7-6(2), 6-3.