A diehard Jets fan was savagely beaten on his own turf by a drunken gang of Kansas City Chiefs fans after their team was trounced on Sunday — with one of the assailants barking “F–k New York” and “You all deserved what happened on 9/11!” the victim’s distraught family told The Post.

James Mohr, 23, a physical education teacher at the Bronx Guild vocational high school, was wearing his Jets gear after the team’s 37-10 victory as he walked through Parking Lot J at MetLife Stadium when a woman standing with a pack of thugs screamed the vile taunts.

Mohr took offense and told the rowdies their 9/11 insult was “disrespectful,” said his sister, Anna Mohr, 28.

“Our other brother is a fireman, and my father is retired FDNY, so you can understand why a 9/11 comment would especially irk him,” Anna said. “He was shocked anyone would actually say something like that.”

Mohr, who lives in Auburndale, Queens, was walking alone from where a group of neighborhood pals had gathered in another part of the lot where some buddies from Manhattan College were parked when he was jumped by up to seven of the cowardly goons. At least one was wearing a Chiefs football jersey, a police source confirmed.

The lifelong Jets fan suffered a fractured jaw, cheekbone and eye socket in the beatdown, and also has bleeding on the brain.

Mohr underwent hours of surgery to repair his shattered face yesterday at Hackensack University Medical Center, where his family was keeping vigil.

“He’s hanging in there and he’s scheduled for surgery. We won’t know too much until that’s done,” Anna Mohr said before surgery.

State troopers originally busted one of the alleged attackers, New Jersey resident Merle Lee, on a simple assault charge, but have since upgraded charges against Lee to aggravated assault after Mohr’s condition worsened.

Mohr’s father said the alcohol-fueled violence is all too common at sporting events and that stadium officials should crack down.

“When we got to the hospital, the people in the ER said, ‘Oh, not another one,’ and told us this happens all the time,” Dan Mohr, 64, said from his son’s bedside.

The elder Mohr — who was an NYPD cop before switching over to the FDNY — compared his son’s attack to the brutal beating of San Francisco Giants fan Brian Stowe, who suffered serious brain injuries from an attack outside Dodger Stadium last March 31.

“It’s very similar to that story that happened in California, and we’re feeling fortunate that he wasn’t hurt more seriously,” Dan Mohr said.

A stadium rep said, “This is an unacceptable attack on one of our guests and we have been working with the New Jersey State Police to make sure the man arrested is prosecuted to the fullest extent of the law.”

With AP