The city's premier annual sporting event returns to Flushing Meadows-Corona Park Monday; with it will come hundreds of thousands of tennis fans, millions of dollars for the Big Apple and, potentially, history on the court.

All eyes will be on Serena Williams at the U.S. Open, as she seeks to become the first person in 27 years to win a calendar-year Grand Slam sweep of tennis' four major tournaments.

"Tennis is in the air in New York," said Juan Andrade, the executive director of the Tennis Innovators program.

The predicted 720,000 spectators will get to see all the action on the hard court at the USTA Billie Jean King National Tennis Center under a "sneak preview" of an eagerly anticipated new amenity: The Arthur Ashe Stadium retractable roof, which is 65% complete and set to provide much needed shade over hot late summer days. It will be fully operational next year.

There will be a nightly light show on the roof, as well.

The U.S. Open isn't just a marquee matchup for tennis, of course. It's incredibly important for businesses throughout Queens and the rest of the city as well.

The USTA said the tournament generates about $800 million in economic impact for the city, a figure which Mark Conrad of the Fordham Business School said surpasses the Super Bowl's impact here in 2014.

"It is still summer, so it's still good to visit New York, so people treat this as a vacation," he said. "It does attract a clientele who has some money to spend."

The most-anticipated matches are hot tickets, of course, but bargain hunters will be in luck on Sept. 10. All doubles matches will be free to the public, including the semifinal rounds for both the men and women competitors.

Fans said they were excited to see their favorite players such as Williams and Rafael Nadal play under the lights. Claudao del Valle, 47, of the Lower East Side, said he looks forward to bringing his 6-year-old son, a big tennis fan, to free doubles day.

"It's a great thing to spend time [at]. He can learn and think about the future of sport," del Valle said.

Conrad said a Williams win would generate a lot of positive buzz for the city and increase the sport's popularity.

"There will be incredible publicity and everyone will be watching," he said.

Danny Zausner, the COO of the tennis center, agreed with that notion. The tournament's true measure of success, he said, is the degree to which it grows fans' affection for the sport and the city the tournament calls home.

"We have two weeks of the best that the sport and New York has to offer. Everyone who spends the day here, leaves enriched," he said.