NEW ORLEANS (AP) — Things had gone so smoothly for New Orleans as it prepared to host the nation’s premier sporting event, the American football championship Super Bowl. Then, with the biggest TV audience of the year watching, the lights suddenly went out.

The outage, blamed on an unspecified “abnormality” in the Superdome stadium’s power system, was an embarrassment for New Orleans, which was hosting its first Super Bowl since 2002 and was eager to show off how it has been rebuilt since Hurricane Katrina.

The Superdome itself was a focal point of the Katrina catastrophe as 15,000 to 20,000 people, who failed to evacuate the city, crowded into the sports stadium that was unprepared to hold them. A lack of water, sanitation, electricity and security quickly turned the stadium into a scene of unspeakable horror.

Mayor Mitch Landrieu called Sunday night’s outage “an unfortunate moment in what has been an otherwise shining Super Bowl week for the city of New Orleans.”

He said he expected to receive “a full after-action report from all parties involved” in the coming days.

The Super Bowl is a major event across the United States akin to the World Cup globally. People gather across the nation for parties to celebrate the game and outside the stadium the parking lots are crowded with partiers grilling barbeque and drinking beer in so-called “tailgate parties.”

The Baltimore Ravens had been cruising along with a 28-6 lead in the game when, without warning, the power to the Superdome suddenly shut down early in the third quarter, plunging parts of the 38-year-old stadium into darkness and leaving TV viewers with no football and no explanation why.

For 34 minutes, the players tried to stay loose, the fans milled about in darkened corridors, and stadium officials scrambled to figure out what went wrong. The Ravens barely hung on for a 34-31 victory over the San Francisco 49ers.

“It really hurt us,” Baltimore player Vonta Leach said. “We had lot of momentum.”

There is sure to be some fallout for the city and the Superdome — especially since New Orleans plans to bid for the title game in 2018, in conjunction with the 300th anniversary of its founding.

Escalators stopped working and credit-card machines shut down, though auxiliary power kept the playing field and concourses from going totally dark.

“We sincerely apologize for the incident,” Superdome spokesman Eric Eagan said.

Most fans seemed to take the outage in stride, even starting up the wave to pass the time.

The problem occurred shortly after Beyonce put on a halftime show that featured extravagant lighting and video effects.

A joint statement from Entergy New Orleans, which provides power to the stadium, and Superdome operator SMG shed some light on the chain of events, although they weren’t sure about the source of the problem. It apparently started at the spot where Entergy feeds power into the stadium’s lines.

“A piece of equipment that is designed to monitor electrical load sensed an abnormality in the system,” the statement said. “Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue. … Entergy and SMG will continue to investigate the root cause of the abnormality.”

The FBI quickly ruled out terrorism, and the New Orleans Fire Department dismissed reports that a fire might have been the cause.

New Orleans was once a regular in the Super Bowl rotation and hopes to regain that status. The Superdome has undergone $336 million in renovations since Katrina ripped its roof in 2005. Billions have been spent sprucing up downtown, the airport, French Quarter and other areas of the city in the past seven years.

Maybe they forgot one of the basics.

Joked Doug Cook, a Ravens fan from New Orleans: “They didn’t pay the light bill.”

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AP Sports Writer Brett Martel and Associated Press writers Brian Schwaner and Kevin McGill in New Orleans contributed to this story.

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Copyright 2013 The Associated Press.