British number one Elena Baltacha battled to a 2-6 7-5 7-6 (7-2) victory over third seed Julia Goerges in the second round of the Texas Open.
With the temperature climbing above 40C, world number 61 Baltacha fought back from a set and a break down to beat the German, ranked 20th.
"Julia plays a very, very fast ball, and I knew I'd have to go for a little bit more than I usually do," she said.
Baltacha, 28, will play Aravane Rezai or Sorana Cirstea in round three.
The Scot is through to the quarter-finals of a WTA tournament for the first time this year and her run of form comes just ahead of the US Open, which starts on Monday.
"It's incredibly hot here and I must admit that it's very, very hard to play in," she said.
"I think New York is going to seem freezing after this but that's what it's all about - making sure I go into the US Open ready for anything."