Petra Kvitova saved four match points before finally knocking third seed Jessica Pegula out of the Indian Wells Masters 6-2, 3-6, 7-6 (11) on Tuesday.
The day session thriller which spilled well into the night hours, landed the double Wimbledon champion into the quarter-finals here for a third time.
The Czech has never been past the last eight at the event in 11 previous appearances.
Victory for the veteran came after two and a quarter hours, with a tight tiebreaker finally deciding the outcome.
“The emotions were up and down,” the winner said. “I don’t know how many match points I saved.
“I still don’t know how I did this.
“I knew Jesscia would not miss, I was always a break down in the third set, I just tried to come back.
“In the tiebreaker you just never know. I had to go for it in the tight moments and that is not always easy.
“But I’m happy in the end.”
Pegula had reached quarters in six of her last seven WTA 1000 tournaments.