Behind the modesty and unassuming humor lay the truth.

Jessica Pegula had not believed. Deep down in her heart she had no firm faith.

But her confidence has grown in the last year. Hell, in the last few weeks.

This meant she reached the final of the US Open on Saturday.

And she hopes it will help her win her first Grand Slam title. No, she is confident that she will succeed.

“If you had told me at the beginning of the year that I would be in the final of the US Open, I would have laughed out loud because that was just my mindset and I didn’t think I would make it here,” admitted Pegula, who will face No. 2 Aryna Sabalenka.

Pegula, whose father Terry owns the Buffalo Bills and is worth $7.7 billion according to Forbes, has been a top-20 player since 2021 but came to Flushing 0-6 in the Grand Slam quarterfinals.

But the foundation for her groundbreaking victory over No. 1 Iga Swiatek was laid long before.

When she broke out of her comfort zone, changed trainers, reshaped her body and improved her flexibility.

Has improved.

“Once you start winning a lot of matches and have the belief in yourself that you can win in difficult moments and beat these girls, it gives you a lot of confidence for those weeks,” said Pegula, 30. “I was able to build on that. Learning through different experiences, winning tournaments, all of that just adds up.

“When you do things and try things and work on them and you can use them in tournaments, you get confident and you think, ‘I can really get better, I can improve and I can hit those shots in the big moments.’ That just builds and can build really quickly. … So, it’s nice. I hope that I can be an inspiration to other players who feel like they’re stuck or not getting better, and that you can always find a way to get better and improve.”

This open-mindedness and drive to improve led him to part ways with his long-time coach David Witt after a loss in the second round of the Australian Open and to hire Mark Knowles and Mark Merklein for the San Diego Open in February.

The boost in confidence was undeniable.

“Yeah, obviously it’s improved a lot,” Knowles told the Post. “She’s been one of the top players for a couple of years and all players want to make the jump to Grand Slam level. She’s a very ambitious young lady and she felt like she had what it takes. But it takes a whole other level of belief. And I think she’s done it. I think she’s really gained that confidence this summer.”

“Her confidence has really grown and it showed throughout the tournament. She had a difficult draw and overcame some difficult situations. She is exactly where she wants to be and she believes she can do it.”

After a few injuries at the beginning of the season, Pegula has worked hard on her conditioning, which has improved her endurance and agility, and this is reflected in her results: an excellent 15-1 record since the Paris Olympics.

“Even Jessica said after Wimbledon, ‘I know I’m playing well.’ You need that combination. Then you need the validation of some results,” Knowles said. “And for her to win the tournament in Canada after the Olympics on a different surface was exactly what she needed. … So when a player gets validation and feels like she’s playing well, that combination builds confidence.”

The victory in Toronto boosted Pegula’s confidence, as did her entry into the final in Cincinnati. There she suffered her only defeat after Paris, a 3-6, 5-7 loss to her opponent from Saturday.

“Yes, it’s a great challenge,” said Knowles. “It’s the final of a Grand Slam. She’s going to give it her all. And you want to play against the best. You have to remember that Sabalenka is probably the best player in the world right now and you want to beat her. This is the ultimate challenge. She’s really looking forward to it.”

And confident about it.