The seventh seed and two-time Grand Slam winner, now the highest-ranked player left in the women's singles draw, was on the back foot from the start against a fourth-seeded opponent who broke her in the opening game.
In truth, Gauff was fighting herself almost as much as the American number one. Playing in the Wimbledon quarter-finals for the first time, she made 17 unforced errors and served four double faults in the opening set.
The 22-year-old got things back under control in the second set, although she still faced two break points in the opening game, and halved the number of unforced errors.
The 2023 U.S. and 2025 French Open winner led for the first time when she broke Pegula in the final set but her older opponent was not beaten yet and broke back to 3-3.
Gauff going the distance in her matches
Gauff, who will face either Naomi Osaka or Karolina Muchova in the semi-finals, replied with another immediate break, then held serve and Pegula fell at the first match point with a return to the net.
"Pretty insane, honestly," was Gauff's immediate reaction to the win. "Considering how I hadn't won a match on grass in two years before this tournament, I'm definitely just really happy with how I played today."
"Jess is an incredible opponent and person and playing against her is never easy. I'm just happy to get through this one today."
Gauff, who has now been taken to three sets in her last four matches and has yet to win a grass tournament, said getting more first serves in was a turning point as well as being calmer in the rallies.
"In the first set I think I made a little bit too many errors rushing out the rallies a little bit too quickly," she said. "I just felt the last two sets were really great tennis."
"I've been going three sets almost every match so I feel like when you have that faith in yourself as a competitor, when the match goes the distance and you lose one set, you're not panicking."
The match was the first between two female American top 10 seeds at Wimbledon since the Williams sisters, Serena and Venus, met in the final in 2009.
"After seven years playing this tournament it's finally the first time I can walk on Centre Court and I didn't feel nervous," said Gauff. "I don't know if I'm becoming a vet ..."
Wimbledon 2026
Wimbledon is taking place from June 29th to July 12th at the All England Club in south-west London. With 128 players in the draw, it is the third of the four Grand Slams of the tennis season and the only one played on grass.
Men's singles draw and results | Women's singles draw and results | All you need to know about the tournament | Find all our Wimbledon coverage here