Thousands took off for the annual Stephen Siller Tunnel to Towers 5K Run & Walk commemorating 9/11 on Sunday morning, just over a week after a series of terror attacks rocked Manhattan and New Jersey.

The runners included about 100 people who weren’t able to race in Seaside Park, New Jersey, last week after a bomb went off.

But as runners took off from the Brooklyn Battery Tunnel on the crisp morning with former Mayor Rudy Giuliani sending them off, and people gathered at the finish line, the mood was festive.

Laura Marko, 50, from Toms River, New Jersey, was about to start the race in Seaside Park last Saturday when she saw smoke. Re-registering for the Tunnel to Towers on Sunday was a no-brainer.

“It really is our new normal, it’s ridiculous. And I never thought a small event like that would be disrupted. I never even thought it was real,” she said about the attacks.

Marko, who said her daughter is a cadet at West Point, said they ran the Tunnel to Towers race last year as well.

“I have absolute confidence in the NYPD and our military,” she said about running Sunday. “I feel great, I’m not afraid at all.”

As runners made their way out of the tunnel on the Manhattan side, more than 300 responders stood, some high-fiving runners and most holding photos of firefighters who died on Sept. 11, 2001.

Later, a moment of silence was held for everyone who died that day, those who became ill after working at Ground Zero, those who went to battle following the attacks, and law officers who were killed defending the city.

Frank Sinatra’s “New York, New York” then played, the large crowd singing the chorus.

The race, in its 15th year, was named for Stephen Siller, 34, an FDNY firefighter who was on his way home that day when he heard of the attacks on the World Trade Center in lower Manhattan. Siller, who was raised in Rockville Centre and graduated from St. Agnes High School, turned around and drove his truck to the entrance of the Battery Tunnel, but it was closed, according to the foundation. He strapped 60 pounds of gear on and ran through the tunnel, dying during the rescue efforts.

The run benefits the Building for America’s Bravest program, which builds smart homes for injured service members.

“This year, especially, felt more poignant,” said Frank Vogt, 40, Siller’s nephew. “I was able to look back and reflect.

“You move on little bits by bits,” he said. “It’s a way to celebrate his passing and everything that happened even though it was a tragedy. Fifteen years is just a number, so really it feels as present as ever. . . . It’s not just about him, it’s about the city.”

Vogt, who lives in upstate Cornwall, said he’s now helping his own kids — 7 and 4 years old — understand what happened.

“They’re asking questions,” he said. “They have their own way of working through it.”

Justin Siller, Siller’s nephew, said what’s more amazing than the 15th anniversary of the run is that it keeps getting bigger every year.

“It means a lot just to see the amount of people that come and show support,” said Siller, 35, who lives in Farmingdale, New Jersey. “It stinks that we lost him, but it wasn’t for nothing.”

As the race wrapped up, thousands gathered on Vesey Street, enjoying burgers, ribs, fruit cups and water. A concert stage played everything from the hits to “God Bless the USA.” Rachel Platten, who sings “Fight Song,” was expected to perform.