SAN DIEGO — The small tennis stadium was packed and in full roar as Daniel Vallverdú watched Casper Ruud and Grigor Dimitrov trade blows and breaks of serve on Saturday.

“Five weeks, we did it all in five weeks,” said Vallverdú, the managing director of the inaugural, and perhaps final, San Diego Open.

Despite the planes that droned overhead, the new tournament did not have much runway: about a month to secure temporary stands and sponsors and then stage an ATP 250 event. These remain extraordinary times for sports and those who attempt to organize them.

The coronavirus pandemic has created upheaval on the tennis tour, canceling tournaments like Wimbledon in 2020 and forcing many events to be rescheduled. But the situation has also generated unexpected opportunity for American cities that would normally have been unable to find a slot on a packed international calendar.

Chicago, once a regular stop on the women’s tour, has staged two new WTA events since August. San Diego, a city with a rich tennis culture, made its debut on the ATP Tour.

“It was one of those things where we were in the right place at the right time,” said Bill Kellogg, one of the San Diego Open’s organizers. “We happened to be in a spot where we could say yes when they asked if we could do it with the China circuit caving in. I know guys that had been trying to get ATP tournaments for years and years and had no luck whatsoever.”

When 2021 tournaments in Asia were canceled because of the pandemic, the men’s tour had vacant space to fill ahead of the BNP Paribas Open tournament in Indian Wells, Calif., a prestigious 12-day event that had been moved from March to October because of the pandemic.

Vallverdú, a former player who has coached top players like Andy Murray and Dimitrov, knew there might be an opportunity in nearby San Diego with its nearly perfect weather and no tour-level event.

Most ATP tournaments hold “sanctions” that guarantee their spot on the tour and that can be sold, just as N.F.L. franchises can be sold. But the ATP Tour has been offering one-year licenses during the pandemic to make up for lost playing opportunities. Thirteen tournaments have operated on these one-year licenses in 2020 and 2021.

Vallverdú contacted his friend Ryan Redondo, the new executive director at the Barnes Tennis Center, a public facility with 25 outdoor courts that is a hub for the junior game.

Redondo, once an all-American tennis player at San Diego State, knew the power of big events firsthand. At age 5, when he attended a 1989 Davis Cup match between France and the United States in San Diego, the playful French star Henri Leconte brought Redondo onto the court for a hit when John McEnroe took a bathroom break.

“Part of my strategic plan and vision was we should have every level of tournament possible here at the Barnes Center, from red ball events for 3-year-olds to ATP and WTA events,” Redondo said. “We need all of that to inspire the kids.”

He spoke with two potential benefactors, Kellogg and Jack McGrory, who thought Redondo had to be talking about 2022, not 2021. But they quickly agreed to become the still-notional tournament’s co-sponsors.

“We said yes in 24 hours, and we had no idea what we were getting into,” McGrory said. “It was much more complicated than we expected.”

McGrory said they got the initial funding for the tournament with a $100,000 grant and $200,000 loan from the Southern California Tennis Association Foundation, of which Kellogg is president. McGrory said they were able to raise $850,000 in sponsorships and contributions and another $800,000 from tickets and concessions. The ATP contributed the prize money of more than $600,000.

“We’re going to be able to pay off the loan and put some money back into the Barnes Center,” McGrory said.

The tournament, with its modest stadium court expanded to 2,000 seats, was sold out for its last four days. Above all, there was a fine field with Murray, a former No. 1, and eight top-20 players: a lineup worthy of a higher-level event than an ATP 250. The proximity to Indian Wells was a big factor in the elite players’ participation, and the winner turned out to be the 10th-ranked Ruud, a Norwegian who has won five titles in his breakout season.

But it remains uncertain, even unlikely, that Ruud will be able to defend his title in San Diego. A one-year license provides no guarantee that the tournament will return to the city. What it does provide is a chance to showcase a new venue.

“I have a lot of titles to defend next year, and I know four of them will be played next year and for this one we will have to see,” Ruud said on Sunday as he cooled down on an exercise bike after his 6-0, 6-2 demolition of Cameron Norrie in the final. “It’s obviously tough. The ATP is hosting over 60 events a year and all over the planet, so it’s not easy to find a week to fit in. This year, San Diego was able to do this in five weeks, so I see no reason why they couldn’t do it again, and I hope they will do it again not just because I won but it was a great city and great weather. These are perfect conditions for us to play in. It’s not too hot, not too humid and great atmosphere.”

San Diego has produced some fine tennis players. Maureen Connolly, who was known as Little Mo, dominated the women’s game in the early 1950s, achieving a Grand Slam by winning all four major singles titles in 1953. Karen Susman won the Wimbledon women’s singles title in 1962. Kelly Jones was ranked No. 1 in the world in men’s doubles in 1992. Recently, CoCo Vandeweghe broke into the women’s top 10 in 2018 and Taylor Fritz reached No. 24 in the ATP singles rankings last year, becoming the top-ranked American man. Brandon Nakashima, ranked 79th at age 20, is one of the most promising American men’s prospects.

But there has never been a main ATP Tour event in San Diego until now, and there has been no tour-level event in San Diego County since the women’s tournament in Carlsbad moved to China in 2014.

The United States, once the mainstay of the men’s and women’s tours, has steadily lost tournaments to Asia and Europe. In recent years, the Indian Wells event has been the only ATP event in California, and none of the biggest West Coast cities have had a regular men’s tour event.

The decline of American tennis has played a role, particularly the decline of American men’s tennis, but the shift also reflects the more global nature of the sport and the new economic strength of Asia.

The pandemic, however, has canceled most Asian events for the last two years, a particularly big blow to the women’s tour, which had moved its year-end championships and much of its late-season lineup to China. The Shanghai Open, one of the top events on the men’s tour, also was canceled in 2020 and 2021.

It remains unclear what approach China will take going forward, just as it remains unclear whether the San Diego Open was a one-off or the first chapter of a long-running tennis story.

But the tournament certainly got the ATP’s attention. Ross Hutchins, the ATP’s chief tour officer, was initially intending to travel straight to Indian Wells from Europe. Instead, after hearing about the buzz at the Barnes Center, he moved up his travel plans and came to San Diego to observe and meet with the tournament’s team.

“It’s a huge credit to them and the tournament how they not only embraced the concept but how they delivered,” Hutchins said Sunday. “And to do it in five weeks and to have the outcome they delivered is phenomenal.”

Potential options for San Diego include buying another tournament’s sanction, persuading the ATP to break longstanding policy and create a new sanction, or negotiating another one-year license.

Nothing is guaranteed, but McGrory sounded confident at Sunday’s awards ceremony as he turned to the finalists.

“This is not going to be their last time here,” he said.