Patrick Mahomes' Fiancée Showers Fans With Champagne After OT Win

Brittany Matthews doused fans in champagne to celebrate the Chiefs' insane win over the Bills ... shaking up a bottle and spraying it all over the crowd from her suite.

Patrick Mahomes' fiancée was fired up like it was the Super Bowl ... celebrating after her man's 8-yard touchdown pass to Travis Kelce in overtime, which sealed a 42-36 victory and a spot in the AFC Championship Game.

Mahomes' little brother, Jackson, caught it all on camera -- showing Matthews unloading the entire bottle on fans in the lower bowl.

No word on how the crowd handled the wet celebration -- after all, it was close to freezing in Kansas City -- but we take it folks were too pumped up to care.

Mahomes finished the game with 378 yards and 3 touchdowns through the air and 69 yards and a TD on the ground.

Britt shared the celebration on her IG ... saying, "Chiefs Kingdom, YALL ROCK🔥💯 #nextround"

The party might continue at Arrowhead Stadium if the Chiefs beat Joe Burrow and the Bengals on Jan. 30.