After nine years as the focal point of a pitched confrontation over urban development, power and basketball, the Barclays Center in Brooklyn began its first day of life on Friday with the hip-hop superstar Jay-Z performing at a sold-out concert while activists outside the arena reminded attendees of the unfulfilled promises of the center’s developer.

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.