Travis Kelce was FUMING on the sideline after the Chiefs fumbled the ball in the red zone, bumping Andy Reid and screaming in his face … nearly knocking the coach on his ass!

The incident went down during the 2nd quarter of the Super Bowl after K.C. star RB Isiah Pacheco turned the ball over deep in Niners territory … a play Kelce watched from the sideline.

The NFL superstar was none too pleased — and expressed his frustration, yelling inches away from his coach’s face — as girlfriend Taylor Swift watched from her suite.

Of course, Kelce and Reid go way back to 2013, when both men joined the organization. Both guys are future Hall of Famers.

It’s not the first time Kelce has lost it on the sideline. Remember back to the Christmas Day game vs. the Raiders when Travis blew his top on the sideline.

Through a quarter and a half, the game has been incredibly tense … with star players on both teams making mistakes.

The 49ers, however, lead 10-0 … after Christian McCaffrey scored a touchdown late in the 1st half.

Kelce has been relatively quiet (besides all the screaming), catching just one ball for one yard. We’ll see if the sideline incident gets him going.