On Monday evening, the first day of the U.S. Open, actors, designers and former professional athletes walked into a side entrance, lined with tennis fans at Arthur Ashe Stadium in Flushing Meadows Corona Park in Queens. They walked a blue carpet, the same color as the famous courts.

A crowd of about 200 people arrived at the tennis tournament’s opening night session several hours early for a fund-raiser for the United States Tennis Association Foundation, which runs tennis and education programs across the country for underprivileged youth. More than $3 million was raised in two hours.

Gabriela Hearst, the fashion designer, showed up with Maria Sharapova, the tennis player. Tommy Haas, a retired player, and Lindsey Vonn, the skier, also attended. Other guests included Mike Tyson, Alec Baldwin, Gayle King, Danny DeVito, Anna Wintour, Vera Wang and Daymond John. David and Cheryl Scharf, New York City philanthropists, hosted a table.

Attendees shared what drew them to the U.S. Open this year.

“The end of summer always makes me a little blue,” said Katie Couric, who was the M.C. for the gala. “By the end of August I always feel depressed, but coming to the U.S. Open gives me something to look forward to.”

“Eating,” said Mr. Tyson, the former professional boxer. “Popcorn, pretzels, all the snacks.”

The crowd headed upstairs for a quick dinner — three courses were served in an hour — and an auction.

At 7 p.m. sharp, guests rushed outside to watch the American sensation Coco Gauff defeat her opponent in a gripping three-set match. Former President Barack Obama and Michelle Obama were spotted at the edge of their seats in another suite.

“There are a lot of wonderful, interesting people who come — I think they are all pretty passionate about the sport, and that is why it’s so fun,” Ms. Couric said, adding, “I mean, when the players are out there you can hear a pin drop.”

Has tennis become more fashionable?

‘I think the players are really enjoying the way they look on court. They have a lot of fun with it.’

Anna Wintour

How did you decide what to wear tonight?

‘It was whatever was in my closet, but it apparently matches the courts, and I didn’t realize that until I got here. I generally tend not to want to blend in with the courts, but I love a good suit, so it’s fine.’

Lindsey Vonn

A few days earlier, on Saturday afternoon, tennis players, devoted fans and financiers descended on the courts of Sportime Amagansett to participate in the 9th Annual Johnny Mac Tennis Project Pro Am tournament and after-party, held in the Hamptons.

“I flew in from Florida for this just because Johnny Mac called,” said Reilly Opelka, an American tennis player, who is not playing in this year’s U.S. Open because of an injury.

“The tennis world and other parts of the world did the same because that’s how it goes,” Mr. Opelka said. “He calls, and you come.”

The event raised more than $625,000, which goes to the Johnny Mac Tennis Project, an organization run by John and Patrick McEnroe that provides tennis scholarships and community programs for New York City-area children.

Seventy-five amateurs bid up to $20,000 to play doubles with former tennis players including Jim Courier, James Blake, Christina McHale, and Mr. Opelka. Popular topics of conversation at water breaks were predictions for Carlos Alcaraz, the Spanish player who is the top seed at the U.S. Open, as well as pickleball bashing.

“Everybody wants to play pickleball, but tennis is still the sport,” said Jeff Zucker, the former president of CNN. “Because you have to be a full athlete to play tennis.”

Participants for the day included: Steve Hasker, C.E.O. of Thomson Reuters; Alex Chantecaille, chief commercial officer of Chantecaille, her family’s beauty brand; and Jean-Yves Fillion, a senior executive at BNP Paribas.

At 6 p.m., when the tournament ended, the players returned home or to the locker room to get ready for the after-party, held at the home of John and Kate Storey, who live most of the year in London, where Mr. Storey is a partner at Goldman Sachs and Ms. Storey is a fashion consultant.

Attendees drank margaritas and tequila sodas, snacked on arancini balls and chicken skewers, and bid on items that included John McEnroe’s personal Wimbledon tickets.

“You know the U.S. Open is starting when this event rolls around,” Mr. Zucker said.

Has tennis become more fashionable?

‘Everyone is tapping into this vintage look, and they are copying looks from the 1970s, but it isn’t 1975 anymore, so it just looks silly.’

Reilly Opelka

Has tennis become more fashionable?

‘Tennis has become such a fashion statement, and we are spoiled for choice at the moment. I love the polo crops and high-waisted skirts that are pleated.’

Kate Storey

How did you decide what to wear to the tournament today?

‘I am from the country club life, so it feels like I can’t wear anything other than white. This year it’s been like, Oh, you can wear pink? That’s OK?’

Alex Chantecaille