Petra Kvitova capitulated from being a set up against Kristyna Pliskova at the WTA Charleston Open as her successful start to 2018 continues to fade to a distant memory.
The two-time former Wimbledon champion won in St Petersburg and Doha in January and February, but Wednesday's 1-6 6-1 6-3 loss to her compatriot came on the back of relatively early exits at the Miami Open and the Indian Wells Masters.
All appeared to be going well for Kvitova as she breezed through the first set, but she lost 11 of the next 13 games as Pliskova assumed complete control.
Kvitova did provide some fight as she rescued half a dozen match points, but her opponent eventually got over the line to set up a last-16 meeting with Elena Vesnina.
Naomi Osaka, full of confidence after her Indian Wells triumph - followed by a defeat of 23-time grand slam champion Serena Williams in Miami - continued her promising form by easing beyond Laura Siegemund 6-3 7-6 (10-8).
The Japanese saved three set points in the second as Siegemund threatened to take the match the distance, before Osaka prevailed in the tie-break to advance to a clash with Julia Goerges, who came from a set down to oust Kristie Ahn 2-6 6-4 7-6 (7-1).
In Monterrey, no singles matches were completed as rain wreaked havoc and washed out play.
Ana Bogdan was leading Sara Sorribes Tormo 6-2 4-3 when the rain set in, with Ana Sofia Sánchez, Sachia Vickery, Magdalena Rybarikova, Jana Fett, Ajla Tomljanovic and Anna Blinkova unable to get on court.