The Montreal Canadiens punched their ticket to the Stanley Cup Finals on Thursday night ... and the fans went absolutely insane!!!
Moments after the Habs defeated the Vegas Golden Knights at the Bell Centre in Canada, thousands of fans swarmed the streets ... and pandemonium ensued.
Cops say fans were just rowdy as hell -- setting off fireworks, fighting and even attacking police officers.
At one point, a group of Habs fans -- still wearing Habs gear -- smashed up a police car and flipped it upside down!!
Police used tear gas to break up the chaos -- and eventually arrested 15 people .