The fourth-seeded Sorana Cirstea, the sixth-seeded Lucie Safarova and the eighth-ranked Karin Knapp had all been beaten on a day of shocks, before the top-seeded Roberta Vinci was toppled in the final match of the day.
The Italian looked in control against Croatia's Ana Konjuh as she took the first set 6-3, but she picked up just four games across the next two sets and was duly dumped out.
The second and third seeds at least got through to give the crowd something to cheer about, with Ana Ivanovic and Kirsten Flipkens both winning.
Ivanovic shaded a tight clash with Alison Riske 7-5 7-6 (7/2), while Belgian Flipkens saw off the promising Puerto Rican Monica Puig 6-4 7-5.
Cirstea's performance was a shocker to start the season with as she took just five games in defeat to Sharon Fichman, with Safarova undone over straight sets by Ayumi Morita.
Knapp took the first set of her match with Julia Georges before losing the next two on tie-breaks to go out, with the day's other game bringing up wins for Kristyna Pliskova against Yanina Wickmayer, Sachie Ishizu against Anett Kontaveit and Lauren Davis against Marina Erakovic.