MLS Star Jay DeMerit -- Foots Bill For Boozy-Canadian Fans, Eh!

You're MLS stud Jay DeMerit and your maple-loving fans just drove 315 miles to see you play -- but your team totally botched the match ... so whadda you do? Buy them a bunch of drinks and get wasted, duh.

TMZ has learned ... the Vancouver Whitecaps captain showed up at a bar called The Vault in Portland, Oregon Saturday night -- after suffering a brutal loss to the Portland Timbers -- and ran into a group of 25 of his BIGGEST fans.

Jay tells TMZ -- he was pretty pissed, but when he saw the fans -- who call themselves "The Handbags"-- he changed his 'tude.

Jay knocked a few back with the group, pounding vodka-sodas, beer and a specialty drink called "The Handbag." In return the group taught him some awesome soccer chants.

The MLS captain covered the $600 tab -- He tells us, "The fans paid a lot of money to travel from Vancouver and if I can give them a good memorable night, then why not?"