60 minutes wasn't enough to decide the NFL season ... and with the Chiefs down 3 after the Niners kicked a field goal in the opening possession of OT, the legendary K.C. QB got the ball, and drove down the field, culminating in a Mecole Hardman touchdown pass.

25-22 Chiefs, game over, Super Bowl over, immortal status achieved for Mahomes and head coach Andy Reid ... who now both have 3 rings apiece, putting them in rarified air.

Mahomes is also a 3x Super Bowl MVP.

It also marks the first time a team has repeated since Tom Brady's New England Patriots did it in 2004 and 2005.

Mahomes threw for 333 yards with 2 touchdowns and an interception ... and was perfect when he needed to be on the last drive of the game -- when his Chiefs needed a field goal to extend the game, or a TD to win.

Travis Kelce had a big second half ... after a slow start to the game, catching 9 balls for 93 yards, including a huge run and catch in overtime.

During the Lombardi Trophy presentation, Kelce said the team wanted 3 straight Super Bowl wins ... so, it's clear they're not done yet.

As the superstar tight end spoke, Taylor Swift and mom Donna Kelce watched in front of the podium ... before Travis came over and shared a lengthy hug and kiss with his GF.

As for the 49ers, they put up a helluva fight ... and Brock Purdy -- who threw for 255 yards and a touchdown -- made some nice plays, especially during his team's lone OT possession.

Unfortunately for San Francisco, Mahomes and the Chiefs were ultimately too much.