Patrick Mahomes' GF Lost Her Damn Mind During Chiefs' Comeback

No one -- on Earth -- was more fired up about the Chiefs' epic comeback against the Houston Texans than Patrick Mahomes' girlfriend, Brittany Mathews ... and it's all on video.

Brittany WENT FULL-ON BERSERK while watching her boyfriend engineer one of the greatest comebacks in NFL playoff history ... screaming, yelling, talking trash!!!

The 23-year-old was watching the game from a VIP suite at Arrowhead Stadium in Kansas City ... surrounded by other Chiefs players' GFs and her BFF Jackson Mahomes, Pat's younger bro.

As the Chiefs started cutting into the Texans 24-0 lead, Matthews could barely believe it -- LOSING HER MIND while Patrick went off on the field.

"THAT'S MY BOYYYYYYYYYYYYY," she yelled from the suite ... adding, "WOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!"

Once it became clear the Chiefs were taking control, Matthews sent a video message to all of her haters ...

"All those people that doubted us and hated on us, that thought we were gonna lose this game? GUESS AGAIN!!!"

Matthews ain't exactly a wallflower at Chiefs games -- she's as loud and rowdy as they come -- which might be why Patriots fans heckled the crap out of her during a regular-season matchup at Gillette Stadium toward the end of the season.

The good news for Brittany ... the Chiefs will be back at Arrowhead next weekend to take on the Tennessee Titans in the AFC Championship game.