Tommy Paul's climb into the Top 40 started with 2021 surge, says coach Brad Stine

WATCH: Tommy Paul hit an early Shot-of-the-Year candidate at the Delray Beach Open last week.

Steady improvement is paying off for American Tommy Paul, who has hit the Top 40 for the first time in his career this week. The 24-year-old Paul reached the semis at Delray Beach in Florida and won his first ATP title at Stockholm to finish the 2021 season.

But the signs of this surge came a little before that, says Paul's coach Brad Stine, who has worked with numerous players including two-time Slam finalist Kevin Anderson and four-time Slam champ Jim Courier.

"He was actually playing very good tennis," Stine told Tennis.com. "In Moscow, St. Petersburg, he was actually playing very, very good tennis, [just] wasn't getting quite as much benefit, and we lost a tight one to Taylor Fritz who played extremely well. Then he lost a tight one against [Marin] Cilic.

"I felt like that was when he really started to have things click in a little bit more, and then Stockholm happened and that was very, very good."

Winning Stockholm required beating the likes of Fritz, Andy Murray, Frances Tiafoe and Denis Shapovalov.

"It was the first time that he's put back-to-back to back to back matches like that together," Stine said. "I wasn't entirely surprised.

"I had mentioned to a couple of buddies of mine, coaching people, like that—I felt that he was on the verge of some type of breakthrough. I wasn't trying to be super-prophetic, and I didn't expect necessarily to win Stockholm. But I did feel that it was right on the edge of something good coming along."

The improvements behind this breakthrough, though, have been even longer in the making. Stine started working with Paul in September in 2019, when he was ranked No. 114. Player and coach "made some pretty extensive technical changes, especially in his forehand," said Stine, noting, "[His] forehand is much different if you look at the mechanics of the forehead now versus when we started."

They're going to stick to the same gradual approach as Paul now looks to climb higher in the rankings.

"Once you get to that point and you're in the Top 10, and you know you're in the hunt and looking for Slams. That's a different animal, you know," said Stine. ''So, if Tommy starts to get to the point where that happens, then our concerns will become a little bit different. But at this point for where he's at, I’m very happy with his progress, and that's what we want to see right now.''

Paul has plenty of company, with several other Americans also moving up through the ranks. Like other coaches, Stine is very positive about the potential of the younger group that announced itself in 2021.

"Those guys all still have a long way to go from where they are, but they're all very, very good players. It’s easy for all of us to try and speculate where they’re gonna be, but there's no doubt—I don’t think that Sebastian Korda has very many holes in his game, I don't think [Brandon] Nakashima has many holes in his game," he said. "You know, Jenson Brooksby is probably one of the mentally toughest guys I've ever seen. His results speak for themselves. It’s been unbelievable what he's done at such an early period just starting on the tour."

Paul is currently No. 39 in the rankings. This week, he is scheduled to play Acapulco, where he’ll face Wimbledon finalist Matteo Berrettini in the first round.