"It's just not good enough," Matthews said postgame, per TSN. "We need to be better and I think it comes from the leadership group. I need to be better. All of us need to be better. We just need to look each other in the eye and hold each other accountable."
The loss was the Leafs' second in their last three games without captain John Tavares, who's ruled out for two weeks with a broken finger suffered Oct. 16.
"It's just been the same thing kind of over and over for us. We haven't been disciplined, we're taking ourselves out of the game with lots of penalties," Matthews said.
The Leafs blew a 3-2 lead to the Columbus Blue Jackets on Monday and didn't perform particularly well against the Bruins in response. Boston controlled 58.38% of shot attempts and 70.27% of scoring chances at five-on-five, according to Natural Stat Trick, and Matthews' line was consistently hemmed in against the vaunted Patrice Bergeron-led top unit.
With the win, Boston leapfrogged Toronto for second spot in the Atlantic Division with 14 points and two games in hand.
The Maple Leafs return to action Friday versus the San Jose Sharks before traveling to Montreal on Saturday to conclude their second back-to-back of the week.