CHARLESTON, S.C. -- Top-seeded Jessica Pegula saved four match points to reach her second consecutive semifinal at the Credit One Charleston Open with a rousing 6-4, 3-6, 7-6 (7) win over No.12 Victoria Azarenka.

This was the kind of exquisite match you’d expect from two accomplished, veteran players -- it was fitting that it ended in an ultimate tiebreak. Azarenka herself saved four match points before a forehand service return flew long.

On a cool, blustery day, this instant classic required 2 hours and 36 minutes. After a run to the quarterfinals in Miami, the 30-year-old American has now won six of her past seven matches.

“I totally let my emotions get me in the end [of regulation], Pegula said in a Tennis Channel interview. “I started the tiebreak super nervous. I blew the match points. I didn’t play horrible, but I went for it.

"Whenever that happens, you start the tiebreak and you feel like you should have already won. It was super windy because it makes your nerves even worse. Nothing feels good. You’re kind of like wobbling all over the place.”

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Next up: No.4 Daria Kasatkina, a 6-7 (4), 6-2, 6-3 winner over surprising Jaqueline Cristian -- in a match that went 2 hours and 42 minutes. Kasatkina forged 20 break points and managed to convert 10 of them.

Pegula is 2-0 against Kasatkina, winning three years ago in Rome and last year in the Tokyo quarterfinals. The match on the clay in Italy, however, was 7-5, 6-3. They were set to meet in the semifinals earlier this year in Adelaide but, citing a gastrointestinal illness, Pegula withdrew.

The win leveled Pegula’s head-to-head with Azarenka at 3-all.

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If Danielle Collins defeats Elise Mertens in the day’s third quarterfinal, that would place two Americans in Saturday’s semifinals. The last time it happened in Charleston was 11 years ago when Venus and Serena Willimas made the final four.

Pegula has experienced some wild swings so far in this tournament. Her longest match of the season -- a third-set tiebreak win over Amanda Anisimova ran 2 hours, 26 minutes -- was followed by the shortest, a 59-minute defeat of Magda Linette.

Playing as the top seed for only the sixth time in her career, Pegula overcame a frisky forehand in the early going and settled down nicely. After a series of twists and turns, the first set came down to two points -- and a matter of inches.

Pegula was serving for the set at 5-4 when Azarenka hit one of her classic backhand winners to score a break point chance. She went for it, but a forehand flew just past the baseline. Azarenka, who stayed in a squat for several seconds, clearly sensed the opportunity missed. Pegula then hit a terrific second serve, which fooled Azarenka into hitting a forehand that wasn’t even close. Pegula’s fabulous crosscourt forehand winner finished it.

The second set turned in the third game when Pegula broke Azarenka at love. The final blow was another crosscourt forehand winner. She consolidated that advantage in the next game, winning five straight points after Azarenka won the first three.

'Oh, it's crap': Pegula's hilarious candor after dramatic win vs. Azarenka

With Azarenka serving at 1-3, Pegula had two break points to open it up, but Azarenka saved them. Five straight games later, she had taken the match into a third set.

The momentum continued, with Azarenka scoring another break and winning her sixth consecutive game. But that was the first of four consecutive breaks to begin the third set, which featured some racquet tosses by both players.

In the end, it was 7-all in the tiebreak when Azarenka’s forehand left her. Two misses gave Pegula the match.

Watch: Pegula's best three match-point saves vs. Azarenka

“Missed a couple of easy returns and I kind of knelt down at 6-3,” Pegula said of the final tiebreak. “I was like, `Shoot, I’m not really feeling this right now. This is not great.’ But I was like, `Play one good point, maybe, get a double fault on her serve and get a free point on your serve,' and it kind of just happened that way.

“And I was able to work my way back in. Then she obviously got real tight, too. I knew if I could keep it closer, I would have a chance. I’m just glad I got through that.”

While this is Pegula’s third semifinal of the season, following Adelaide and San Diego, she has never won a clay-court title -- but she’s come close. Pegula lost in last year’s semifinal here to Belinda Bencic. Two years ago, she was a finalist in Madrid, falling to Ons Jabeur.