Dad duty saved his life on 9/11.

Nassau County Executive Bruce Blakeman — a top official with the Port Authority of New York and New Jersey when terrorists struck the World Trade Center on Sept. 11, 2001 — acknowledged Sunday “by the grace of God go I.”

At the time, Blakeman, 67, served as a commissioner on the Port Authority of New York’s governing board and chaired its public safety committee — appointed by then-Gov. George Pataki.

Blakeman on Sunday recounted that he was scheduled to meet with “my friend” PA executive director Neil Levin at the Windows of the World restaurant on the 106th and 107th floors of the North Tower that Tuesday 22 years ago.

But a commitment to be with his son intervened, and he told the Post he rescheduled that breakfast meeting for two days later.

“I took my son Arlen to school that day,” said Blakeman, reflecting on the worst terrorist attack in America’s history, with Al Qaeda hijackers crashing planes into the two World Trade Center towers, collapsing both of them.

“I think about that all the time. I think about my friend Neil Levin,” the Nassau County leader said..

The Port Authority was the landlord of the WTC towers.

Eighty-four its employees died in the attacks, among them 37 members of the bi-state agency’s police department.

Blakeman also suffered a profound personal loss that day along with the deaths of professional colleagues.

He recounted that his nephew, Tom Jurgens, a 26-year-old state court officer who also was Army veteran and volunteer firefighter, went to help evacuate workers at the South Tower. Jurgens died when the towers collapsed.

“They never found his body. Only his pistol and shield,” Blakeman said.

The county exec said he goes down to the WTC memorial every year to pay his respects during the reading of names of all the Ground Zero victims.

“That’s my nephew’s final resting place,” said Blakeman. “It doesn’t get any easier. It’s heartbreaking every year. It’s an open wound.

“And it makes me angry that the people killed were robbed of having children, grandchildren.”

Blakeman said he’ll also attend the Nassau County memorial ceremony held at the Harry Chapin theater in Eisenhower Park at 6 p.m. Monday.

He said after he got a call from the PA about the towers getting hit, he drove down to assist.

But the calamity worsened: The PA’s emergency command center was in the WTC complex, as was New York City government’s. They were destroyed when the towers collapsed.

PA officials scrambled and initially relocated at the Metropolitan Transportation Authority’s emergency center in Grand Central terminal, he said.

Meanwhile, his brother, Brad Blakeman, who was deputy assistant to then-President George W. Bush, helped evacuate the president and other White House officials to an undisclosed location.

“It was a baptism by fire. It was a horrible, horrible time,” Blakeman said.

PA commissioners, who oversaw the WTC complex, had to make numerous emergency decisions in the days and weeks after to aid search, recovery and rebuilding efforts, he added.

“We were in shock for a month. For the first few weeks, we were robotic. We had to make important decisions,” he said.