Under weeping, sun-starved skies, the surrounding streets were animated from early morning. Curiosity-seekers without tickets staked out viewing spots in hopes of glimpsing notables and to bear witness to a milestone.

“We thought Beyoncé was going to come out the side,” said Josie Mignone, 68, a lifelong Brooklyn resident who walked over to the center with her husband from their nearby apartment 11 hours before the start of the concert. After making a few detours to weigh bargains at some stores, they planted themselves in the Starbucks on the arena’s ground floor and had some free samples.

“This is a big event for us Brooklyn people,” Ms. Mignone said.

By early afternoon, dozens of workers were filing through a back door, many of them reporting for their first day of a new job.

There had been a frenzied push to complete the arena in time for this night, and even hours before the doors opened, hurried preparations were still going on. Ladders were evident everywhere, as workers scrambled up them to fiddle with light fixtures. Other workers were carting in big steel racks filled with bottles of red wine and high-priced vodkas. Larry Banks, 19, from Ridgewood, Queens, arrived to do janitorial work, probably restroom duty, still unsure of the assignment.

“It’s history right here,” he said. “And I’m working, keeping it together.”

Dozens of opponents staged protests throughout the day. At dusk, thousands arrived to see the show — to hear a superstar rapper who grew up in a Brooklyn housing project. Many wore T-shirts and caps that suggested the new arena’s role in invigorating pride in this borough.

Then there was Daphne Carr, 34, uncomfortably straddling two worlds. She slept outside the arena on Thursday night and held a sign: “Brooklyn Sold but We Ain’t Buying.” But unlike other protesters who have sworn never to enter the Barclays Center for an event, she acknowledged with a shrug that she was attending Jay-Z’s concert on Saturday.

“It makes me complicit in a world of evil,” she said. “I know that.”

But she said she got tickets free and was a quiet connoisseur of Jay-Z’s music.

This was more than an inaugural concert. It was also a demarcation point in a searing battle that took on the contours of a morality play.

The long-delayed $1 billion arena — which as the home of the transplanted Brooklyn Nets returns a major-league sports team to Brooklyn for the first time in more than half a century — has become a metaphor for the trials of change in an already changing borough.

More than 14,000 fans representing a broad assemblage of people funneled into the center. At the insistence of Jay-Z, nearly half of the tickets were priced at $29.50, plus fees, while choice seats sold on the resale market for thousands of dollars. The true upper end were the 11 superluxurious floor-level suites, known as the Vault, which lease for $550,000 a year, with a three-year minimum contract.

The developer Bruce C. Ratner watched from one luxury suite, while Mikhail Prokohorov, the Russian billionaire who owns the Nets, occupied his own suite. Most of the Nets players attended, many of them at the invitation of Deron Williams, the star point guard, who has a luxury suite as well.

The arena left little free of corporate sponsorship. There were phone-charging booths from MetroPCS and entrances named for Geico and EmblemHealth. Women in gowns handed out $5 gift certificates to the Foxwoods casino.
 

The crowd was growing fidgety as the lights finally dimmed at almost 9:45. A slide show recounted aspects of Brooklyn’s history, including the Brooklyn Bridge, the Beastie Boys, Ebbets Field and finally the Brooklyn Nets. Jay-Z took the stage in a white Nets hat and a black Nets jersey — No. 4, with “Carter,” his actual last name, across the back. Before a projection of city projects, he said, “Today is a celebration, a celebration of the place where I’m from. When I say, ‘Is Brooklyn in the house,’ I want to hear everybody. Is Brooklyn in the house?” The crowd roared.

Meanwhile, many residents of the surrounding neighborhoods of Park Slope, Prospect Heights, Fort Greene and Boerum Hill remained apprehensive about the arena’s opening.

The swooping glass-and-rusted-steel structure, at the intersection of Atlantic and Flatbush Avenues in the heart of New York’s most populous borough, is the first element of a proposed $4.9 billion, heavily taxpayer-subsidizedAtlantic Yards development, the biggest ever tried in Brooklyn. The project is designed to squeeze 15 housing towers and a possible hotel or commercial building onto a 22-acre plot, adding thousands of permanent jobs and affordable housing units.

Yet none of the other buildings have risen, and many concerns persist about them and the levers used along the way by Mr. Ratner and his Forest City Ratner Companies.

Forest City Ratner, which also built the headquarters of The New York Times in Midtown, imagines completion of the project may span 25 years, far more than its original 10-year estimate. Groundbreaking on the first residential tower is scheduled for December.

After so much queasiness and competing prophecies of just what it will mean to put a big arena on this Brooklyn plot, the concert was the first chance to see how it works. Would the traffic be impossible? Would the food satisfy the borough’s increasingly exacting standards? Would drunken fans wake up sleeping families and their dogs? Would enough people come?

But before any of those questions could be answered, the protests — a staple of the construction zone for years — went on.

The protests outside the center throughout Friday were, for the most part, modest in size and often included farce as a means of expression. They involved a news conference beneath the entrance canopy, sermons, bits of street theater and coordinated Twitter posts.

The demonstrators, some of whom slept on the street the night before, rarely numbered more than 50.

Several women, done up in outlandish wigs, rhinestone jewelry and garish sunglasses, wore sandwich boards that said: “Billionaires for Barclays. Who’s in Your Pocket?”

The activist performer Reverend Billy of the Church of Stop Shopping appeared in a white suit, white boots and clerical collar and lamented that “Bruce Ratner figures” are destroying neighborhoods around the world.

About 6:30, a small group of protesters spied Marty Markowitz, the Brooklyn borough president, heading toward a side entrance. They chased him down the block shouting, “You can’t negotiate with a monopolist!”

In reaction to the protesters, Joe DePlasco, a spokesman for Mr. Ratner, said, “We are 100 percent committed to the affordable housing, jobs and other benefits of Atlantic Yards and welcome those who were against them at the start to work with us to achieve them going forward.”

Jay-Z, who will perform eight concerts to open the Barclays Center, has left his imprint throughout the project. He has leveraged his tiny stake in the Brooklyn Nets and the arena into an outsize presence as one of the public faces of the project, including helping design the team’s insignia and uniforms. He also owns an upscale club called 40/40 inside the center.

The Nets are the center’s principal tenant, the first major sports team in Brooklyn since the Dodgers broke the borough’s heart by leaving for the West Coast in 1957. On Oct. 15, the Nets will play their initial preseason game at the 18,200-seat arena, and on Nov. 1, they will take to the court to start the basketball season against the Knicks, from the borough next door.
 

Marcus Bruny, 24, a security guard from Canarsie, was unconflicted. He arrived for the concert wearing a Nets jersey, Nets jacket and Nets hat. “It’s only right,” he said. “I’m going hard for Brooklyn, that’s where I’m from.”

To get a sense of the center’s impact, Stephen Levin, a city councilman, patrolled the blocks around the arena with constituents as concertgoers arrived. In the hours before the doors opened, though, traffic on the main avenues did not seem unusually heavy. One fan who drove to the arena said he had no trouble parking four blocks away.

At one point, a Columbia University class on urban design collected outside the front entrance to contemplate the stew of issues the new building raised.

Local businesses near the center, any number of which have gravitated to the area recently, were keen on attracting the extra passers-by for themselves.

At the Italian restaurant Va Beh’, an extra worker had been recruited for the evening to prepare pasta. The place expected to remain open as late as 1 a.m., two hours later than customary.

A neighbor, Yayo’s Latin Cuisine, planned on an even longer night, because of a different concern. It operates a small parking lot across the street for its customers.

“Even friends are going to come here and say, ‘I’ll have dinner, leave my car there, go to the Barclays Center,’ “ said Robert Garcia, the manager. “That’s not going to happen.”

Mr. Garcia said the restaurant had assigned two bouncers to guard the lot.