Ground Zero was never an easy place for Jerry D’Amadeo, whose father was killed on 9/11.

But on the 15th anniversary of the terrorist attacks, the East Patchogue resident commanded the space — starting Sunday’s memorial ceremony in lower Manhattan with a salute to his dad, Deer Park native Vincent Gerard D’Amadeo, 36, a vice president at Cantor Fitzgerald who died in the north tower.

“In the beginning it was kind of tough just being here,” D’Amadeo, 25, said after he had spoken to the crowd of about 8,000. “Now I come here and am able to just think about memories, the good times I had with my dad.”

Because his father’s body was never recovered, D’Amadeo, who now volunteers at the National September 11 Memorial Museum, said that being at the World Trade Center regularly has helped him heal.

“For me, it’s a place of closure,” he said.

Nearly 500 Long Islanders were among the almost 3,000 people killed in the attacks on Sept. 11, 2001.

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Sunday’s ceremony on the grounds of the 8-acre World Trade Center site included many of the rituals of ceremonies past: the display of a tattered flag from the site, the singing of the national anthem and the tolling of a bell at the moments when tragedy struck.

The minutes are etched in collective memory:

8:46 a.m., when American Airlines Flight 11 struck the north tower.

9:03 a.m., when United Airlines Flight 175 hit the south tower.

9:37 a.m., when American Flight 77 struck the Pentagon.

9:59 a.m., when the south tower fell.

10:03 a.m., when United Flight 93 crashed near Shanksville, Pennsylvania.

And, the last, at 10:28 a.m., when the north tower collapsed.

The names of the victims were read by family members — some who came bearing flowers and carrying photographs — in a ritual, punctuated by tears, that lasted nearly four hours.

The ceremony attracted dignitaries and politicians, including presidential candidates Hillary Clinton, a Democrat, and Republican Donald Trump.

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Clinton, who left the ceremony early, was captured on video stumbling as she was assisted into a waiting sport utility vehicle by Secret Service agents. Her campaign issued a statement saying the candidate felt “overheated” and had retreated to her daughter Chelsea Clinton’s Manhattan apartment, where she was “feeling much better.”

The campaign later issued an additional statement, disclosing the candidate had been diagnosed with pneumonia two days before.

Trump left the ceremony shortly after 10:30 a.m., following the last moment of silence.

Other officials attending included Gov. Andrew M. Cuomo, Mayor Bill de Blasio, former mayors Rudy Giuliani and Michael Bloomberg, Rep. Peter King (R-Seaford), Sens. Chuck Schumer (D-N.Y.) and Kirsten Gillibrand (D-N.Y.) and New Jersey Gov. Chris Christie.

Thousands also attended remembrance ceremonies in Nassau and Suffolk counties on Sunday, which included a sunrise memorial service at Town Park at Point Lookout and a parade down Main Street in Islip.

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At Ground Zero, a spray of water rose from the rim of the cascading waterfalls that mark the towers’ twin footprints. There, 82-year-old Judith Jones said she felt her son’s presence.

“There was a spray from the pools making us feel like he was there,” Jones, of Livingston, New Jersey, said of her son, Donald T. Jones II. The 39-year-old Cantor Fitzgerald employee died in the north tower on 9/11.

“Then there was a rainbow and it just took my breath away,” she said. “It’s a good day for us. We feel closure.”

George Oates, a Lindenhurst firefighter who says he contracted cancer from volunteering in the cleanup effort at Ground Zero in the aftermath of the attack, wore his dress uniform to the memorial site.

“Fifteen years — it’s like the day it happened, or the first time they had the anniversary,” said Oates, 66, who has battled skin and rectal cancers since his diagnosis in 2007 and walks with a cane.

Vickie Belcher, 41, of Centereach was there to remember her friend, firefighter Michael Joseph Cawley, 32, of North Bellmore. Cawley was with Rescue Co. 4, but covered a shift for a friend with Engine Co. 292. When the call came in on 9/11, he went to the scene.

Belcher said Michael’s friends have come every year since 2002. “We see the rebirth,” she said. “You see the same hurt and pain. It’s getting a little easier seeing the rebirth. Obviously there’s hope.”

“We can’t share our memories of Michael, but we can laugh at them,” Belcher said. “He was just a great all-around person.”

Meanwhile, Cuomo on Sunday issued a two-year extension for 9/11 workers and volunteers to seek medical benefits, and also announced plans for a monument to first responders to be built somewhere in New York City.

“We will never forget and you will never be alone,” Cuomo said, addressing first responders at the announcement. “And those are not just words. That is our solemn vow that we will do whatever we have to do and no amount of red tape and no amount of bureaucracy is gonna stop us from being there one for another, especially the people we lost on 9/11 and the hundreds and hundreds of people who helped on 9/11 and have gotten sick since.”

President Barack Obama observed a moment of silence at the White House to mark the moment the first plane hit the Twin Towers, and later spoke at a wreath-laying ceremony at the Pentagon.

“We resolve to continue doing everything in our power to protect this country that we love,” Obama said.

Roberto Labrador, 49, of Park Slope, Brooklyn, attended this year’s ceremony — his first. He heard and saw the first explosion of the north tower and through the years opted to leave the city on the anniversary every year to be with friends instead of revisiting the memories.

“I was here and heard that sound that didn’t sound right. It seemed like my whole field of vision shook when I turned my head and saw the fireball,” said Labrador, a Brooklyn real estate agent and volunteer EMT.

Labrador helped people in shock in the minutes after the attacks and called into the fog of dust after the buildings fell, asking if anyone needed help.

Sept. 11 was a lesson in the “human spirit to help each other,” he said. “There were people carrying people to safety.”

Labrador has continued to live in the spirit of community through a group called GoRuck — military parlance for deployment — that builds a connection between military personnel and civilians.

About 100 members from across the nation held American flags, fire hoses and backpacks weighing at least 30 pounds at Sunday’s ceremony to acknowledge the weight of gear FDNY firefighters carried that day when rushing into the Twin Towers. On Sept. 11, 343 firefighters died at Ground Zero.

John Grapes, 33, of East Meadow, a member of GoRuck who works for the Nassau County Sheriff’s Department, stood outside with others in front of the FDNY Engine 10 Ladder 10 firehouse, which once faced the World Trade Center.

“For me it’s to never forget and to be true to the sacrifices made. I remember as a New Yorker and a Long Islander,” he said.

The photo and typed story of fallen firefighter Jeffrey Olsen of Staten Island was secured on his backpack.

“I know his wife and I want to remember that he gave his life when he ran into the towers to save other people,” Grapes said. “I feel we should come out to honor all the fallen.”