It began with a human traffic jam and could end with a Grand Slam. There were unprecedented and initially confusing medical requirements and a massive storm that stranded spectators and flooded courts. Some of the game’s biggest stars did not play, but a host of intriguing new ones took advantage of their absence and electrified audiences that seemed to make more noise than ever.

The 2021 U.S. Open has by no means been normal. Attendance is down and the competition is up, but amid a fluctuating pandemic, it has been a notable milestone on the road to tennis, and perhaps civic, normality.

“Everything has been a little bit less,” said Margaret Zuba, a tennis fan and actuary from Marlboro, N.J. “Less crowds, less intensity. But the tennis has been great and it’s really nice and relaxed. Yes, we have to wear masks indoors. Yes, we have to be vaccinated. But we can deal with that.”

Zuba is one of the more than 522,000 people who have attended the annual event in Queens in the first 10 days. That figure is down 19 percent from the record-setting attendance mark set in 2019, when more than 737,000 went through the gates. The United States Tennis Association attributes some of the loss to the pandemic and the reluctance of many to travel, particularly internationally.

The absences of Serena and Venus Williams, Roger Federer, Rafael Nadal and the defending men’s singles champion Dominic Thiem, who all skipped the event because of various injuries, may also have contributed to the diminished attendance, too.

“In the first two quarters of the year we were planning on only being able to have 25 or 50 percent capacity,” said Michael Dowse, the U.S.T.A.’s chief executive. “So, given everything that is going on, we are extremely happy with how that has gone. And tennis-wise, it has been great. ”

That is especially so for some players looking to take advantage of the vacuum of absent superstars. While tournament organizers, fans and vendors hoping to get their money might miss the likes of Federer and Nadal, the players who did show up were not whining about it.

“I don’t care if Roger or Rafa are here,” said Daniil Medvedev, the second-ranked man. “I want to win the tournament.”

Frances Tiafoe, an American ranked 50th, said he saw fellow players in the locker room, “foaming in the mouth,” at the prospect of advancing without having to contend with three of the game’s best players. “Pretty funny to watch,” he added. “I’m in the locker room cracking up.”

Fans gathering to see players like Medvedev, Tiafoe and the world No. 1 Novak Djokovic had to show proof of vaccination against the coronavirus, a rule that was implemented only three days before the start of the tournament at the insistence of Mayor Bill de Blasio of New York. Dowse said the ticket refund process has shown that some fans elected not to attend before the vaccine mandate, but he believes others bought tickets once they heard of the rule change.

Dowse said roughly 7,500 coronavirus tests had been administered to players, staff and entourage members, through Thursday. Of those, only 0.47 percent returned positive, he said, and all of them were upon their initial entry to the tournament, which he said indicated the event was not contributing to a spread of the virus among players and staff.

Fans were not tested.

“It’s always awkward now, with Covid,” said Rob Segal, a health technology entrepreneur and tennis fan from Manhattan who attended with his school-aged son. “But we’ve felt safe. It’s felt kind of normal.”

But on Aug. 30, the first day fans were allowed into the grounds, thousands were caught up in a maddening, two-hour wait in to get inside during the midday heat. The foul-up was caused by understaffing and a lack of training at the gates. By the next day, additional workers were assigned and the problem appeared to have been solved.

Once inside, fans witnessed some early upsets, the continued success of a legion of Canadian players and the emergence of three compelling teenagers. They included Canada’s Leylah Fernandez, who upset the defending women’s singles champion Naomi Osaka, Emma Raducanu of Britain and the Spaniard Carlos Alcaraz, who upended No. 3 Stefanos Tsitsipas.

Fernandez and Raducanu will meet in an all-teenage women’s final on Saturday, with Raducanu becoming the first qualifier into a major final in the Open era.

The buzz surrounding the teenagers energized fans and made veteran players, like the 28-year-old American Shelby Rogers, take note. Rogers was asked for her advice to the hard-charging youngsters.

“Buckle up,” she said. “It’s a long ride.”

But no one was prepared for what happened on the third day of the tournament when the remnants of Hurricane Ida ripped through the region. The storm caused massive destruction and dangerous conditions, including at the Billie Jean King National Tennis Center. The tournament was caught off guard and organizers were criticized for not calling off the night session and sending fans home well before the deluge.

A few hundred fans and workers, including the No. 16 seed Angelique Kerber, were forced to wait out the storm under the roof of Arthur Ashe Stadium (or inside the gym, where Kerber stayed until 4 a.m.), while others faced potentially risky rides home in flooded areas.

“We didn’t cancel because in meeting with the state of New York and our meteorologists, it was projected as a heavy rainstorm,” Dowse said. “And we’ve done extremely well, heavy rainstorm for years.”

But this turned out to be different, and many were caught by surprise. Dowse had left the grounds before the storm but returned at 5:30 the next morning to find several courts flooded. He said there was several feet of standing water in the outdoor grandstand and Court 17. But they were pumped out and after a one-hour delay, the tournament resumed under sunny skies.

Later that night, Djokovic won his second match of the tournament, over Tallon Griekspoor. He has since advanced to a semifinal against No. 4 Alexander Zverev, as he continues his quest for a Grand Slam. Djokovic won the Australian Open, the French Open and Wimbledon already this year and a title on Sunday would make him the first man to win a Grand Slam (all four major tournaments in the same calendar year) since Rod Laver in 1969.

It would also give him a record 21 major titles, one more than Federer and Nadal. After he beat the sixth-seeded Matteo Berrettini in a quarterfinal on Wednesday night, he declined to talk about the Grand Slam in an on-court interview.

“I know that a lot of people want to hear me talking about it,” Djokovic said later. “But let’s talk about it, hopefully on Sunday.”

There would be nothing normal about that.