Katie Boulter survived a real scare against compatriot Sonay Kartal to maintain her hopes of winning a third successive Lexus Nottingham Open title.
Boulter, who was replaced this week as British number one by Emma Raducanu, won her maiden WTA Tour title in Nottingham two years ago and backed it up last summer.
And she extended her winning run in the city to 12 matches with a 6-4 1-6 7-5 victory over British number three Kartal.
Boulter trailed 4-2 in the deciding set and had to save a break point to avoid going a double break behind, with the eighth seed struggling in the heat and consulting the doctor.
But she rallied impressively to make it through to a quarter-final against American McCartney Kessler.
"I have so much respect for Sonay, she is such a tough competitor and I also know she's never going to give me anything at any point," said Boulter on the BBC.
"I know she's going to surpass me at some point, she's got the game for it, she's got the head for it. I'm going to have to face that fact.
"But at the very end I just wanted to grit my teeth as hard as I possibly could and get myself over the line. I'm really pleased with myself today. It wasn't easy, for sure.
"I feel like I step into my house when I come onto this court. I have such great vibes here but the heat was killing me today.
"I am definitely proper British because I can't handle the heat at all. I'm just glad I got over the line."
Boulter looked very comfortable on serve all through the opening set but Kartal took control at the start of the second set, winning five games in a row.
The 23-year-old appeared to be heading for victory midway through the decider, with Boulter looking spent, but she roused herself and put aside the disappointment of missing two match points at 5-4, clinching victory two games later.
Boulter is the only British player left in the draw after teenager Mimi Xu lost 7-5 6-1 to sixth seed Magda Linette.
The 17-year-old, who will make her Wimbledon debut later this month after being given a wild card, won her first WTA Tour match in the first round before sitting an A level biology exam on Wednesday.
She pushed Linette, ranked 31st in the world, very hard in the opening set but the Pole used her experience to come through a series of close games in the second.
