The celebration all went down Monday night, after Tampa Bay earned a 4-2 series victory over the Stars ... and the scene was wild!!!

Lightning players poured a grip of champagne and beer into Lord Stanley -- and then got after it ... opening their throats and throwing booze straight down the hatch.

Check out video of the celly ... winger Pat Maroon and defenseman Kevin Shattenkirk were the chugging all-stars -- while others on the squad enjoyed some sips from the cup as well.

And, we know what you're thinking ... but NHL players have been locked away in a bubble with daily COVID testing the last couple months -- so this is all safe!!!

Of course, the Lightning earned every bit of this moment ... they were heartbreakingly swept out of the playoffs last season despite being the favorite, so the win Monday meant a helluva lot.

But, some Lightning fans weren't as careful as the players with their Cup parties ... take a look at people PACKING the streets in Tampa to celebrate the win.