Garbine Muguruza was soundly beaten by Magdalena Rybarikova at the Aegon Classic on Monday as the ninth seed became the biggest casualty of the opening day.
Muguruza failed to win either of her opening two service games and, even after triumphing in her third, dropped her fourth, with her wastefulness eventually punished by Rybarikova.
And the Spaniard's serve continued to let her down in the second - dropping three more games as Rybarikova soared to a 6-3 6-1 victory.
Muguruza was not alone in becoming the victim of a day-one upset in Birmingham, though, as 11th seed Alize Cornet allowed her lead to slip in a 4-6 6-2 6-2 defeat to Christina McHale.
Cornet recovered from losing on her own serve in the opening game to go a set up, but was not so lucky in the second after falling 4-0 behind.
McHale came out with the advantage from a remarkable run of five games without a hold from either player at the beginning of the third and produced one further break for good measure to wrap up the win.
Wildcard Naomi Broady pulled off one of the results of the day, beating world number 81 Ajla Tomljanovic 6-3 6-4 to set up a second-round clash with top seed Simona Halep.
Other home hopes Johanna Konta and Katie Swan experienced mixed fortunes, with the former thumping Jarmila Gajdosova 6-1 6-3 and the latter beaten 6-2 6-2 by Tsvetana Pironkova.
Konta now faces sixth seed Karolina Pliskova, while fourth seed Angelique Kerber awaits Pironkova.
Second seed Ana Ivanovic is set to take on Portugal's Michelle Larcher de Brito, who defeated Zheng Saisai 6-3 6-2.
Elsewhere, there were wins for Casey Dellacqua, Lucie Hradecka, Klara Koukalova, Katerina Siniakova and Anna Karolina Schmiedlova against Lauren Davis, Lesia Tsurenko, Coco Vandeweghe, Kurumi Nara and Bojana Jovanovski respectively.