Down 5-4 in the first set against qualifier Olga Govortsova, Halep won five straight games to take the first set and go up an early break in the second. She eventually went on to a 7-5, 6-2 triumph, converting on three of four break points while fighting off the only one on her serve. She also improved to 4-0 against the Belarusian.
No.2 seed Dominika Cibulkova was not as fortunate, as Yaroslava Shvedova upended her, 6-2, 3-6, 6-3. Though it was a big upset on paper, Shvedova actually has now beaten the 10th-ranked Slovak three times in six encounters. This was Shvedova's sixth Top 10 win and first since surprising Caroline Wozniacki at Madrid in May 2013.
"It was a tough match against a tough opponent," Shvedova said. "It's a good first match on grass for us and good preparation for Wimbledon. I'm glad we put on a good match in front of a lot of people."
Next up for Shvedova is Dutch wildcard and 2006 's-Hertogenbosch champ Michaella Krajicek.
"I'm happy that I played well today," Shvedova said. "My serve was working very well. Hopefully, tomorrow I can continue this."
"I tried to get to the net more and take the ball earlier," King said. "I think by making myself try to come to the net more, I was more aggressive on all of my shots."
No.4 seed Carla Suárez Navarro was a 6-4, 6-2 winner in her opener against last week's Birmingham runner-up, Barbora Zahlavova Strycova. Her sixth win in seven clashes with the Czech was her 35th of the year - two behind Ana Ivanovic for most on the WTA.
Securing quarterfinal berths were seventh-seeded Garbiñe Muguruza and Magdalena Rybarikova. Muguruza bested Yvonne Meusburger, 6-4, 6-1, and Rybarikova improved to 3-0 against fifth-seeded Andrea Petkovic with a 6-4, 6-7, 7-5 win that lasted two hours and 54 minutes.