Reigning Aegon International champion Dominika Cibulkova suffered a surprise second-round exit at the hands of home hope Heather Watson on Monday.
Watson sprung a shock on the fourth seed, prevailing 7-5 6-4 in the pick of the results on an action-packed day at the WTA Premier event in Eastbourne.
With Wimbledon looming, it was a huge confidence boost for the wildcard, who is ranked 126th in the world and faces Anastasia Pavlyuchenkova next.
"I'm so grateful for everyone who came out and supported today," said Watson, who took her fourth match point. "The atmosphere was incredible and I was getting goosebumps at the end there.
"It's no secret that I got a little nervous, but I'm very pleased that I got through it in that last game."
Most of the other seeds in action had no such troubles, with Karolina Pliskova (3) defeating Alison Riske 6-4 6-3 and French Open champion Jelena Ostapenko (10) shrugging off a second-set collapse to down Carla Suarez Navarro 6-3 0-6 6-4.
Pavlyuchenkova, seeded 14th, overcame Elise Mertens, but Daria Gavrilova (16) was beaten by qualifier Lara Arruabarrena.
Other winners included Lauren Davis, Barbora Strycova and Kristyna Pliskova.