Urszula Radwanska failed to follow up her victory over Venus Williams with another win at the French Open.
By losing 6-3, 6-3 to German qualifier Dinah Pfizenmaier on Wednesday, the 40th-ranked Radwanska also missed out on a chance to face her older sister, No. 4-seeded Agnieszka, in the third round at Roland Garros.
Urszula Radwanska has never made it past the second round in 13 appearances at Grand Slam tournaments.
She began the French Open by beating the 30th-seeded Williams, a seven-time major champion, 7-6 (5), 6-7 (4), 6-4 on Sunday. But on Wednesday, Radwanska lost five of the first six games against the 127th-ranked Pfizenmaier, who finished with a 33-6 edge in winners in her third career Grand Slam match.
Agnieszka beat American Mallory Burdette on Wednesday.