The 29-year-old Rybáriková, a semifinalist at Wimbledon last year, fell to a shock 3-6 6-1 5-7 defeat by Barthel, who will face either defending champion Donna Vekić or Vera Lapko in the quarterfinals.

Japanese third seed Naomi Osaka recorded a dominant 6-3 6-2 win over Czech Republic’s Denisa Allertová in just over an hour to reach her first WTA quarter-final on grass, where she will take on rising Romanian Mihaela Buzărnescu.

Buzărnescu had her best-ever Grand Slam run at the French Open earlier this month, where she reached the last 16, and continued her good form by beating American Irina Falconi 6-3 5-7 6-3 in the second round.

Slovenian Dalila Jakupović strolled to a 6-4 6-3 win over Poland’s Magdalena Fręch to book a quarterfinal berth against the winner of the all-British showdown between Johanna Konta and Heather Watson, which will be played on Thursday.