Fourth-seed Petra Kvitova's stuttering form continued at the Madrid Open as she reached the third round with a 6-4, 2-6, 6-3 win against CoCo Vandeweghe.
The hard-hitting Czech, who missed the Indian Wells and Miami tournaments because of exhaustion and suffered a first-round exit on indoor clay in Stuttgart last month, was in control when she lead by a set and 2 1
American world number 36 Vandeweghe then took five games in a row to turn the match on its head and stood toe to toe with the Wimbledon champion in the decider before faltering.
However, there were no alarms for defending champion Maria Sharapova as she crushed Colombia's Mariana Duque-Marino 6-1, 6-2.
Former runner-up Victoria Azarenka set up a third-round clash with top-seed Serena Williams with a 6-3 6-3 defeat of Croatian Ajla Tomljanovic.
In the men's draw, tenth-seed Grigor Dimitrov was 6-4 3-0 ahead when American opponent Donald Young quit with an injury while Gael Monfils dropped only two games against Serbian Viktor Troicki.