Dustin Poirier’s emphatic victory over Conor McGregor at the beginning of the year goes down on their ledgers as “TKO (punches).”

That’s true enough. Poirier unleashed a barrage of fists that McGregor barely withstood before appearing to lose consciousness following a gnarly right hook.

But those who witnessed the Jan. 24 rematch in Abu Dhabi, United Arab Emirates, which preceded Saturday’s upcoming UFC 264 ESPN+ pay-per-view rubber match between the two standout lightweights at T-Mobile Arena in Las Vegas, saw the real key to victory for Poirier: calf kicks.

The lower leg strike, which may appear innocuous enough to casual fans, has been all the rage in mixed martial arts in recent years. It’s the catalyst behind a rise in leg kick TKOs in the UFC, underscoring its effect as a fight-ending weapon even without attacking heavy to the head or body.

Despite hype over calf kicks reaching drinking-game levels on near-weekly fight cards, UFC color commentator and recently retired 155-pound fighter Paul Felder believes McGregor and his team were caught with their pants down in terms of respecting the strike’s potency.

“The fact that Conor thought he was just gonna check it just shows me that they really weren’t aware of how dangerous that kick is until he was in there in that particular fight,” Felder recently told The Post, “because, if you’ve been hit with a few of them, for real, even in sparring, you know, ‘Oh, God damn, I can’t let that become a thing. I’ve gotta figure out a way around that kick.’”

Poirier landed several calf kicks throughout the first round of their second fight — a rematch of McGregor’s first-round TKO when the two were up-and-coming featherweights in 2014. Although Poirier lost the round on the judges’ scorecards as the Irishman got the better of a competitive round, the kicks reddened McGregor’s calf and laid the groundwork for what was to come. 

Opening with a heavy calf kick to start the second frame, Poirier stumbled McGregor briefly, a sign of the cumulative damage to the lead right leg of the former two-division champion. And they kept coming, affecting the movement of McGregor and often buckling him as the outside of his calf changed its hue. One minute into the round, Felder declared on the broadcast, “That leg is crushed right now.”

By the time McGregor began to catch Poirier’s foot — after the calf kicks had already landed — it was too late. The damage was done, and it allowed Poirier to open up further on what had already been some success with his punches going back to the first round. With McGregor’s mobility severely compromised, Poirier opened up with big hooks to an opponent trapped against the fence. By the 2:32 mark, McGregor was side-sleeping from the punishing punches.

“That calf kick is such a game changer,” said Felder, who went 17-6 as a pro and said he once lobbied to fight Poirier, a fighter and man for whom he has great respect.

“I know it’s kind of something that you hear us analysts harp on a little too much. From someone who has been hit with them, it shuts down your whole leg and changes the outcome of a whole fight with maybe three kicks.”

Poirier landed 18 leg strikes, according to UFC Stats, with the bulk of them being calf kicks. If three kicks is enough to compromise the common peroneal nerve — the primary objective when attacking the calf — it’s easy to see why at least three times that number would disable McGregor to such a degree. 

Felder suspects McGregor’s ongoing affair with boxing contributed to losing sight of the calf kick’s rise to ubiquity in the sport.

“I think that, unfortunately for Conor, since at that point he had been away from competing regularly and being in the scene and being around MMA, he’s doing a lot of other stuff, I think [calf kicks] kind of slipped past him a little bit,” Felder said. “Maybe he didn’t have respect for it because he hasn’t been in there getting hit with it.”

That’s no longer the case, and Felder wonders if McGregor will adopt them into his arsenal as he and Poirier close their trilogy. 

“They’re not gonna go and evolve their whole games from the last time they fought,” Felder says. “They’re gonna be similar athletes to what they were, but how they approach it can be different.

“And for Conor, that’s gonna come down to: What’s he gonna do with these calf kicks? Is he now gonna adopt them into his game? Is he gonna go back to that more elusive style, that karate style of movement, in and out, throwing crazy kicks? Are we gonna see more of that?”