Bethanie Mattek-Sands produced a shock in the first round of the Generali Ladies tournament in Linz on Tuesday.
The 201st-ranked American beat seventh seed Tamira Paszek of Austria 6-2 6-4, converting her third match point when Paszek double-faulted.
Her reward is a second round clash with Carla Suarez Navarro of Spain, who defeated Slovakia's Magdalena Rybarikova 6-3 6-4.
Mallory Burdette of the United States also progressed into the second round with a 6-3 6-4 win over Ksenia Pervak of Kazakhstan.
Pervak had lost in qualifying but replaced 2009 champion Yanina Wickmayer of Belgium, who pulled out shortly before the match because of exhaustion.
Dominika Cibulkova of Slovakia, who was seeded third and reached the final last year, also withdrew from the event with a shoulder injury.
Fifth-seeded German Julia Goerges beat 2007 champion Daniela Hantuchova of Slovakia 6-4 7-6 (7-5) after rallying from 5-3 down in the second set.
She will next play Romina Oprandi of Switzerland, who routed Alexandra Cadantu of Romania 6-2 6-1.