The curtain came down on the U.S. Open on Sunday night, with the men’s final and Novak Djokovic grabbing history.

But Monday morning the USTA surely is already looking to the future, and that future looks brighter than it did a year ago.

When Serena Williams rode off into the retirement sunset and took her 23 Grand Slam titles with her, it was fair to ask of American tennis: What’s next?

But these two weeks showed what was next.

It showed 19-year-old Coco Gauff breaking through with her first major title, the youngest American to win the title in Flushing Meadows since her idol Williams back in 1999.

It was over the past two weeks in New York that Gauff not only made her dreams come true but made American tennis hopes real.

“I think the three words I’d put it in is ‘Dreams come true,’ ” Gauff said in the afterglow of her win. “I don’t think it can be put into words. But there’s a song lyric I want to use for my Instagram caption. It goes, ‘Concrete jungle, where dreams are made of.’ Yeah, that lyric is true. New York City is the city where dreams are made of.”

Channeling her inner Jay-Z and Alicia Keys, Gauff was in an Empire State of Mind. But so is American tennis.

“It speaks to the importance of having American champions,” USTA Player Development GM Martin Blackman told The Post.

Much has been made about no American man having won a Grand Slam since Andy Roddick did it in 2003. Twenty years and counting.

But U.S. Open quarterfinalists Francis Tiafoe and Taylor Fritz were both ranked in the top 10, and after serving his way into the semis versus Djokovic, unseeded 20-year-old Ben Shelton could join Tommy Paul in the top 20 on Monday.

The men’s game is looking healthier than it has in years. The women’s game, with Gauff and third-ranked Jessica Pegula, is positively thriving.

“The bar is at the top. For American tennis, the goal for American tennis will always be to be the best in the world, and to win Grand Slams. It will always be,” Blackman said. “Now, are we going to go back to a time when we completely dominated the rankings? No, because the game is global. … But [the goal] is always going to be domination.

“So when we look at and evaluate how we’re doing versus the rest of the world, we have different segments that are a combination of age and ranking. Certain benchmarks are hit when players are 14, 16, 18, 21. We look at those segments, and we see how many players do we have in that segment in terms of age and ranking versus the rest of the world? And our goal is to be number one in every category.”

As of June 19, the U.S. was No. 1 in players ranked in the top 100 of both the WTA (15) and ATP (11). But more to the point, the numbers are trending up.

Robin Montgomery — a product of the Junior Tennis Championship Center that produced Tiafoe — is a teen who won the 2021 U.S. Open girls’ singles title.

Clervie Ngounoue, just 17, won this year’s Wimbledon junior title and climbed to the top of the ITF Junior Circuit world rankings in June.

The U.S. tops all countries in the WTA U-21 Top 225 with 10. When the USTA sits back after the curtain comes down on this tourney, they’ll like what it sees