Mahomes sat out the second quarter when he headed down into the locker room and was listed as questionable due to an injury suffered at the end of the first, but returned heavily strapped up as the Chiefs claimed a place in the AFC Championship Game for the fifth straight season.
The MVP candidate revealed after the game that he had undergone X-rays in the locker room in the second quarter that cleared him to return, offering him confidence he will be available next weekend too.
"The X-rays were negative," Mahomes told NBC. "They haven’t diagnosed anything yet. But I'll be good to go [for the AFC Championship Game]."
"I did not want to go [to the locker room]. They gave me the ultimatum that I wasn’t going back in, unless I went in there. They were trying to take care of me, we've got a lot of great people over here. But it will take a lot to keep me out of the football game."
The Chiefs will face either the Buffalo Bills or the Cincinnati Bengals in the AFC Championship Game, with those two sides to do battle on Sunday. If the Bills win, the game will be played in neutral Atlanta, while a Bengals victory will make the host Kansas City.
Mahomes soldiered on in the second half against the Jags, improving his Divisional Round record to 5-0, finishing the game with 22-of-30 passing for 195 yards with two touchdowns.
The quarterback threw a jump TD pass for Marquez Valdes-Scantling to open up a 10-point fourth-quarter lead after the Jags had rallied back to 20-17.
"It's a credit to the guys around me," Mahomes said. "The offensive line kept me clean in the pocket knowing I couldn’t move. The guys made plays around me.
"That's what a great team does, when somebody gets a little banged up, everybody else steps up."
Chiefs wide receiver Travis Kelce, who had 14 catches for 98 yards with two touchdowns, said he feared the worst when Mahomes went down.
"You don’t want to go down the train of thinking the worst but you automatically do," he said. "He's our fearless leader, we goes, he goes. Even when he had to step out, he was still on that sideline making sure we're still good."
Mahomes and Andy Reid are now joint second for most consecutive Conference Championship Game appearances by a quarterback-head coach duo with five, alongside Ken Stabler and John Madden. New England's Tom Brady and Bill Belichick have the most with eight from 2011 to 2018.