The American fourth seed -- a beaten finalist in New York last year -- saw off Barbora Krejcikova 6-3, 6-3 and is yet to drop a set at the tournament.

"I think I've been playing some really good tennis," Pegula said after dispatching two-time Grand Slam champion Krejcikova inside Arthur Ashe Stadium.

"It's crazy to feel this comfortable on the biggest court in the world with the craziest crowd and the best players. It's something that 10 years ago I never thought I'd be good at this but I guess I am."

Pegula will play reigning US Open champion Aryna Sabalenka or former Wimbledon winner Marketa Vondrousova on Thursday for a place in the final.

The 31-year-old suffered a dismal first-round loss at Wimbledon last month and struggled in the build-up to the US Open, but she has got back on track at the season's final Grand Slam.

"I guess I surprised myself," said Pegula.

"I think, at the end of the day, I always come back to the fact that I'm pretty confident with who I am, and I think I'll always back myself and figure things out in the end instead of kind of spiralling and letting it go too far.

"I mean, I definitely do that a little bit, but I think I always catch myself just in time."

Pegula has yet to face a seeded player at Flushing Meadows.

"I've gotten somewhat of a favourable draw leading up to today," she said.

"I think I haven't really had to play anyone like matchup-wise as well that has really bothered me a ton, so I think that's helped."

Krejcikova pulled off a miraculous escape in the last 16 when she saved eight match points against Taylor Townsend but ran out of steam against Pegula.

"We all saw what she did against Taylor, so I was happy that we're done," said Pegula.