The team managing to tie up the game 2 to 2 in the second period but a Gatineau goal with 10 minutes left in the 3rd period sealed the Sea Dog's fate.
Sea Dogs Head Coach Gerard Gallant says the nerves of winning the President's Cup in front of a sold-out crowd got to the team.
He says it's a dangerous situation as Gatineau now has momentum.
The Sea Dogs lead the series 3 game to 2 as they travel to Gatineau for game 6 on Sunday.
