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Jesse Vargas (27-1, 10 by knockout) isn’t supposed to beat boxing legend Manny Pacquiao (58-6-2, 38 knockouts) when the two step into the ring in Las Vegas on Saturday night with the WBO welterweight belt on the line.

The narrative being painted on social media in the build-up to this fight is that the 27-year-old Mexican-American titleholder has little chance against the veteran Pacquiao, one of the greats of the last few decades.

It will be a fun fight, the thinking goes, while it lasts. But those writing Vargas off have not been paying attention to the young man’s recent rise.

In the last three years, only one of the two boxers has scored a knockout, and that’s Vargas in his last bout, against the tough, then-undefeated Sadam Ali, which won him the vacant WBO title.

The only knockout scored in a Pacquiao fight since 2009 was when Juan Manuel Márquez landed a right that put the Pac-Man down in the sixth round of their fourth fight in 2012.

Now, Vargas is no Márquez. The Mexican warrior faced Pacquiao over 36 hard rounds across three grueling fights before that fight and had to survive six rounds of a beating before timing that right hand perfectly.

Vargas will not have the luxury of having that much shared space and ring time with his more experienced foe.

But Vargas believes in the power of his right hand.

A massive right hand out of nowhere in the 12th round should have saved Vargas from his only defeat, a unanimous decision loss to then-WBO champ Timothy Bradley in June 2015.

After getting dominated for most of the night, Vargas hurt Bradley with that shot, sending him stumbling across the ring with several seconds remaining.

He chased Bradley, hoping to knock him out, but referee Pat Russell mistook the 10-second warning for the final bell and stopped the fight prematurely.

Vargas celebrated what he thought was a TKO, but instead the decision went to the judges, and Bradley retained his championship by unanimous decision.

After Bradley vacated the belt in order to face Pacquiao a third time, Vargas got a second chance at the title. That powerful right made its return against Ali, dropping him twice before the fight was stopped in the 9th round.

Vargas, of course, may have a harder time landing that right against Pacquiao’s awkward angles, often downplayed boxing skills and fast inside-outside combinations, but it doesn’t take more than one Vargas punch to change the direction of a fight.

Will Pacquiao allow that to happen? Well, it depends.

If the Pac-Man boxes in a more careful style like he did against Brandon Rios in 2013 in his first fight after the Márquez knockout, Vargas is likely to lose, getting shut out on the scorecards.

That won’t happen.

It’s been years since the Márquez knockout, and Pacquiao will want to impress.

A firefight will break out, and, if it does, Vargas will have plenty of opportunity to connect.

Come Nov. 5, don’t be too surprised if a right hand from the champ closes the curtain on a legend’s career.