MIAMI, FL, USA - No.5 seed Jelena Ostapenko braved the elements and lateness of the hour - not to mention the fearsome play of No.9 seed Petra Kvitova - to win, 7-6(4), 6-3, and reach her first quarterfinal at the Miami Open.

"It’s not easy," Ostapenko told Andrew Krasny during her on-court interview. "It’s 1AM, we’re still on court finishing the match. Of course, I was fighting hard for this match because when we went off court, I was losing. I just said, ‘OK, I’m going to try my best because I know Petra is a great player and I have to play on a very high level.’ But I’m very glad with how I finished the match."

The last match of the night had barely begun when raindrops kept Ostapenko and Kvitova from commencing the coin toss. Once things got underway, the reigning French Open champion took the upper hand, earning a 4-1 lead and later holding a set point before the two-time Wimbledon champion turned the tables to lead by a mini-break in the ensuing tie-break.

"She was hitting very hard from the beginning," she later explained to WTA Insider. "The first set started good from my side, but she was playing very aggressively and very deep, so for me, it was hard to hit winners off those balls. I was just trying to manage somehow."

Mother Nature intervened once more, sending the players off court until just after midnight when Ostapenko won five of the final six points of the sudden death to sneak off with the opening set.

Kvitova had dropped just two games to Ostapenko at the St. Petersburg Ladies Trophy back in February, but the tricky conditions combined with the Latvian's fearless play ultimately unwound the former World No.2, who surrendered a double fault to bring up match point that Ostapenko converted to take the match in ostensibly one hour and 43 minutes.

"The conditions were so different [in St. Petersburg] and she played great that week, winning the tournament. She beat so many good players in straight sets, even against me, where I felt I wasn’t playing badly but she played unbelievably. I expected a similar level against her today, but the conditions were much tougher. I think she prefers to play indoors, but I was ready for the match.

"I think I was very stable in my legs. I knew she would attack my second serve, so I was ready to somehow hit it back!"

Up next for the World No.5 is fourth seed Elina Svitolina in what will be a rematch of their fourth-round encounter at Wimbledon, which Ostapenko won in two tight sets.

"I played her last year at Wimbledon so I know how she plays. I really have nothing to lose. I think I’m getting back into form, getting more consistent. Winning tie-breaks like this one and the one yesterday [against Haddad Maia] gives you confidence, and you start to feel better."