Heather Watson has beaten beat Belgian Yanina Wickmayer 3-6 7-5 6-3 over two-and-a-half hours.
The British number two battled superbly to see off Wickmayer, ranked 22 places higher at 47, and reach the fourth round in Miami for the first time.
Watson saved five break points across her final two service games in the second set to level the match and served impressively in the decider.
The combination of heat and humidity was so testing the players required a change of clothing before the final set.
"We actually went to the porta-potties - that's where the referees took us - and we both had to get changed in there because we were just drenched," said Watson, who plays Romanian fifth seed Simona Halep next.
And on a day when Spain's Rafael Nadal had to retire because of the extreme conditions, Watson was back out for a doubles match later in the day (she was beaten in that one)
"I've surprised myself," she said afterwards. "I'm actually feeling fine right now, but when I get to my hotel and lie down for a second, I'm probably going to pass out!"
She plays Simona Halep in the fourth round and that will be a tough challenge.