Initial excitement turned to anguish as a raucous crowd watching the game on a giant screen outside Air Canada Centre saw their team let a solid lead slip away during the final minutes of the third period only to be beaten by the Bruins 5-4 in overtime.
Many in the sea of blue and white jerseys packed into Maple Leaf Square in downtown Toronto appeared utterly deflated at the final buzzer in Boston which marked the crushing end of the Leafs' first Game 7 since 2004.
"This is just unacceptable to me," said 18-year-old Jake Roulston. "I've waiting half my life for this game, nine years, for this game, and they blew it, in Game 7. I mean, that hurts."
James Park, who had been cheering on the Leafs until the very end, couldn't believe the game's incredible turnaround.
"This is messed up, we were up 4-1. We lost it all," he said.
"Disappointed millions, the whole city. But we brought a fight, we'll be back next year."
That dogged faith in the team, despite the rollercoaster of emotions it had subjected fans to on Monday night, rose above the disquiet as the crowd shuffled home.
"There's no point in getting angry," said Nicole Cheetham, who had painted a miniature of the team's logo on her face. "The Leafs are a young team and I hope they can get them next year. I'm still a beLeafer."
In analysing the loss, some gave credit to the Bruins for their ability to come back from a three-goal deficit.
"Boston's a good team," admitted Randy Bains, as he held up a Maple Leaf flag. "But you know what, the boys put in a good effort... and I guarantee, four years, we've got the cup."
Indeed, for some, despite the disappointment, there was simply no taming of Maple Leaf pride.
"Blue and white in my veins. Pure blue and white," yelled Justin Allen, who, in addition to his Leafs jersey, had painted his face in his team's colours and was also sporting a blue and white wig.
"It's the history, you have no choice, you gotta believe, you have to."
Harman Singh, who donned a bright blue spandex body suit which enveloped him from head to toe, continued to determinedly wave his Maple Leafs flag and cheer on his team through his megaphone long after most of the crowd had gone home.
"After nine years we came a long way and all I got to say is that we're going to be in the same spot next year same time but we're going to take it this time for sure," said the 20-year-old.
"Leafs fans are known to be the number one fans in the world. Regardless if you win or not, we're still a Leafs fan no matter what."
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