The 29-year-old Rybarikova, a semi-finalist at Wimbledon last year, fell to a shock 3-6 6-1 5-7 defeat by Barthel, who will face either defending champion Donna Vekic or Belarusian Vera Lapko in the quarter-finals.

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Japanese third seed Naomi Osaka recorded a dominant 6-3 6-2 win over Czech Republic's Denisa Allertova in just over an hour to reach her first WTA quarter-final on grass, where she will take on rising Romanian Mihaela Buzarnescu.
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Naomi Osaka of Japan returns a shot to Denisa Allertova of Czech Republic during Day five of the Nature Valley Open at Nottingham Tennis Centre on June 13, 2018 in Nottingham, United Kingdom.

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Buzarnescu 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 Jakupovic strolled to a 6-4 6-3 win over Poland's Magdalena Frech to book a quarter-final berth against the winner of the all-British showdown between Johanna Konta and Heather Watson, which will be played on Thursday.
Australian top seed Ashleigh Barty will also be in action on Thursday as she battles for a quarter-final berth against China's Yin Duan.
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