From the moment the first ball is tossed up at the U.S. Open on Monday, there will be plenty of drama.

From Novak Djokovic chasing immortality to Coco Gauff’s title defense to the rise of the American men, storylines and subplots abound.

After winning her first-ever Grand Slam last year in Flushing, Gauff is back, but can the 20-year-old go back-to-back?

And the American men — with five contenders ranked in the top 20 — are out to snap a 21-year drought without a major title.

But the biggest story of all might be the biggest star of all: Djokovic.

Winning an Olympic gold not only cemented Djokovic as the GOAT of men’s tennis but also gave him what he called the best feeling in his career.

But despite no man defending his title here since 2008, with a record 25th major on the line, Djokovic vowed there will be no hangover from Paris.

“People ask me, ‘Now that you have basically won everything with the gold medal, what else is there to win?’ I still feel the drive. I still have the competitive spirit. I still want to make more history and enjoy myself on the tour,” said Djokovic, 37. “Grand Slams are the pillars of our sport.

“They’re the most important historical tennis events we have, so if you don’t get pumped and inspired to play your best tennis at Grand Slams, it’s hard to do that anywhere else. … Night sessions at the U.S. Open are very famous. I’m going to play my first match here Monday night, so I can’t wait to be under the lights. The noise, the energy of the stadium is just different from anything else. I look forward to it.”

The Serb has caught some breaks before the Open, with Rafael Nadal not competing and No. 1 Jannik Sinner and No. 3 Carlos Alcaraz in the top half of the draw, meaning Djokovic will need to beat just one to win.

Both he and Alcaraz cut short practice sessions — Djokovic on Friday and Alcaraz on Saturday — but both appear 100 percent.

And even though they can’t meet until the final, that possibility of yet another rematch is tantalizing.

Djokovic tore his right meniscus in June at the French Open, but came back in a brace to reach the Wimbledon final, where he fell to Alcaraz.

He turned the tables in Paris in the most satisfying win of his life — and one of the few tough defeats of the Spaniard’s.

“This is one of the most important finals of my career, of my life. It was a difficult moment to deal for me, losing the gold medal in a really close match that I had opportunities,” Alcaraz said. “I try to keep going, try to learn about this match. Just the next finals or the next important matches of my career, I’m going to deal in a different way or a better way than I did in Olympics.”

Gauff became a world star after her win here, carrying the flag at the Olympics and getting her own Wheaties box.

But she had a teary exit at Wimbledon, is just 1-2 since Paris and lost her opener at the Cincinnati Open.

Can she rediscover her old form in Flushing, where Iga Swiatek and Aryna Sabalenka are the top two seeds?

Gauff and No. 6 Jessica Pegula, who won the Canadian Open and reached the final in Cincinnati, lead a strong U.S. charge.

For the first time since 1996, the American men and women both have five players in the top 20: Danielle Collins, Emma Navarro and Madison Keys rounding out the women, and Taylor Fritz, Ben Shelton, Tommy Paul, Sebastian Korda and Frances Tiafoe the men.

Meanwhile, two-time champ Naomi Osaka makes her Open return from maternity leave.

“I made a promise to myself to be as confident as I can in the fact that I am who I am … throughout the year I’ve had really hard matches and it dipped my confidence a little,” said Osaka, who grew up on Long Island.

“I do think coming to this specific tournament helps me out. But whenever I step foot here I don’t really think about the two tournaments I won. I just think about how I felt when I was a kid, because I did grow up coming here and I have such vivid memories of watching my favorite players. It’s more of a childhood nostalgia that I really enjoy.”