Moments before halftime in San Francisco’s divisional round playoff game against Dallas in January, Mike McGlinchey went viral.

Rarely does an offensive lineman rocket around the internet for positive reasons, and this was no exception.

Sliding up the field to try to slow Cowboys All-Pro Micah Parsons, McGlinchey forfeited just enough balance in search of speed that Parsons got his right arm under McGlinchey’s left armpit and sent him airborne. For many on social media, the sum total of the moment amounted to reacting to the video clip or still image freezing 80 inches and 310 pounds of right tackle essentially horizontal with the ground.

Back at his alma mater, though, the moment resonated in a different way. Notre Dame offensive line coach Harry Heistand made sure of it.

Just weeks from announcing his retirement after four decades of coaching, Hiestand showed his pupils the play. Then he showed the 49ers punching home a fourth-quarter touchdown run behind McGlinchey’s double-team block in their 19-12 victory.

“That’s the mental toughness it takes in the NFL,” Heistand told The Post. “You’re going to have bad plays because you’re blocking the best athletes in the world. People can take those little clips and run them back and forth and critique a guy all day, which is total (garbage). But the measure of a player — the measure of any of us — is when you get down and something doesn’t go your way, how do you handle it?

“I showed (Notre Dame’s linemen) those two plays and I said, ‘This is reality. This happens in life. It happens in football. You get knocked down. What are you going to do about it?’ Mike, later in the game, they rip a gap play right behind him for a touchdown in a playoff game. Everybody wants to talk about that play, but to me the measure of him is the next play because those plays happen to every- one.”

McGlinchey’s 49ers, of course, saw their season end the next week in the NFC title game against Philadelphia when rookie Brock Purdy suffered an elbow injury and they finally ran out of quarterback options. Before that, San Francisco had won 12 straight.

Now, after five years in San Francisco, he’s on to the next chapter of his career, agreeing last week to a five-year contract with the Broncos, worth up to $87.5 million, that makes him one of the highest-paid right tackles in the NFL.

He provides what new head coach Sean Payton wants on the field in Denver — mental toughness, run game production and playoff experience — and will likely be one of the pillars in building what Payton promised would be, “a completely different type of culture.”

‘Senator McGlinchey’

In 2019, San Francisco head coach Kyle Shanahan said that McGlinchey, a Philadelphia native, “acted like the CEO of a company the first time he walked in” the 49ers facility as a rookie the year before.

That sounded familiar to Hunter Bivin.

Bivin and McGlinchey arrived at Notre Dame together as offensive linemen in June 2013 and lived together for the next five years. Apprised of Shanahan’s words, Bivin, now the school’s assistant athletic director for alumni relations, let loose a knowing laugh.

“I call him ‘Senator McGlinchey,’ ” Bivin said. “He’s got a career in public service whenever his football career is over with. It’s just a devout love for people, the people that he’s around, specifically. He cares about the people in his circle — he’s my best friend in the world — and wherever he’s at, regardless of where it is, he’s full go. There’s no ‘I’m 50% into being in Denver.’ He’s ‘I’m a Bronco for life.’ …

“That’s kind of his mantra, ‘full tilt, full time.’”

Hiestand posited that part of his disposition comes from the fact that McGlinchey grew up in a huge family. He’s got five siblings and the Irish Catholic family tree goes to triple digits quickly when you include the likes of aunts, uncles and cousins, including first-cousin and longtime NFL quarterback Matt Ryan.

“He’s really a catalyst for your team,” Hiestand said. “… It’s not about me. My success will come when we have success. Mike knew that growing up. He had a big family and nobody’s any more important than anybody else. He grew up in that environment and it was a natural progression as an offensive lineman, to be a guy that cares more about the unit and the team than himself.”

‘Mauler in the run game’

McGlinchey is less diplomatic when a ball carrier is looking for room to work behind him.

“Him being a mauler in the run game, that’s staple Mike McGlinchey,” Bivin said.

It’s been his on-field calling card for years. He turned into one of the NFL’s best right tackles under Shanahan and offensive line coach Chris Foerster.

“’Rock solid’ is the way I’d describe him,” former Notre Dame offensive lineman Mike Golic Jr. said.