British number two Heather Watson dug deep to win 6-4 7-5 against Italy's Camila Giorgi at a rain-affected Aegon Classic in Birmingham.
Their first-round match did not start until after 17:00 BST as downpours delayed the day's play until 15:30.
Watson claimed the only break point of the first set, then saw off six break points for Giorgi in the second.
The world number 55, ranked 11 places higher than Giorgi, will play Barbora Strycova or Karolina Pliskova next.
"I was very focused at the end and I'm so glad we got to play the full match without any rain delays," said 24-year-old Watson.