After linemate Colton Orr got him the puck at the edge of the crease early in the third period, McLaren found himself running out of room. Trying to go to the backhand, he ended up tucking the puck between his legs, off his right skate and through the legs of Bruins goalie Anton Khudobin 1:34 into the third.
It was his third goal of the season and the fourth of his NHL career and extended Toronto's lead to 3-0.
"You've got to work to be in the lineup every night and I've sat (out) a couple of the last few games," the 6-foot-5, 230-pound McLaren said. "Any time you can contribute, especially on the scoresheet and it turns out to be a game-winner, it's a good confidence boost. "
McLaren was clearly enjoying talking about scoring rather than knocking an opponent out with one punch, as he did earlier this season when he floored Ottawa's Dave Dziurzynski.
The Bruins and Maple Leafs meet again Monday night in Boston.
"We have three more periods in a very tough building where we haven't had success before and it's going to take a more intense effort than we had tonight to go in there and have success," Toronto coach Randy Carlyle said.
The Bruins had won their last eight games against the Leafs, dating back to the 2010-11 season. Toronto's last victory over Boston was March 31, 2011 -- 4-3 in a shootout.
"We were getting pretty sick and tired of it so I'm glad we changed that tonight," said Toronto's Nazem Kadri, who continued his hot hand with the opening goal.
The Leafs made the most of their limited chances as they had four shots in the first period, five in the second and four in the third but managed to score a goal in each.
"It wasn't there for the first 40 (minutes)," Seidenberg said. "But when we did get desperate you see how we can play. It doesn't really help playing that way when you're down 3-0. We got to start playing that way at the beginning of the game."
The Bruins wrapped up their four-game road trip at 1-3-0 while totaling just five goals and going 0 for 9 on the power play.
Kadri, who came into the game 10th in league scoring with 33 points (13 goals, 20 assists), has three goals and six assists in his last four games.
Toronto, which came into the game having won just one of its last seven, looked sloppy for much of the evening. Still, the Leafs somehow emerged with two points.
"The bottom line is we won the hockey game," said Toronto captain Dion Phaneuf. "It's a big win for our team. ... Now we refocus, we regroup and we get ready for Monday."
Kadri opened the scoring at 4:58 of the first with his 14th of the season, beating Khudobin on a low shot after receiving a nifty pass from Clarke MacArthur that under Seidenberg's stick.
The goal marked the first time Toronto had led Boston since Oct. 20, 2011 when Dave Steckel scored the opening goal in a 6-2 loss.
Two seconds after the ensuing faceoff, Orr and Shawn Thornton squared off with the Leafs bruiser winning a lengthy fight.
Grabovski made it 2-0 on Toronto's first shot of the second period at 2:52 after flying past Milan Lucic. It was his eighth goal of the season and second in two games after a 10-game drought.
Boston coach Claude Julien replaced Khudobin with Tukka Rask after McLaren made it 3-0.
"The way we gave up the three goals -- they were mistakes," said Julien. "The last goal was a weak goal and I had to give our team a jolt somehow, so I put Tuukka in there and we seemed to turn the corner and play a bit more of our game, but we shouldn't wait for that to happen."
Boston got on the board at 2:30 of the third when Seidenberg's shot from the point trickled through a screened Reimer. The Bruins came on hard after that, hitting the post twice.
Ference cut the lead to 3-2 with 1:16 remaining and Rask on the bench for an extra attacker.
Toronto's Liles left the game in the second period after a sliding Daniel Paille hit him at the boards. He suffered what was termed a lower-body injury and did not return.
Carlyle said X-rays were negative, meaning it was more of a sprain than anything broken or torn.
The Leafs honored former captain Mats Sundin before the game. Sundin, a member of the 2012 Hockey Hall of Fame induction class who was slated to be feted during one of the games eliminated by the lockout, dropped the ceremonial puck. Fans showed the big Swede lots of love every time he was shown on the video screen.
Copyright by STATS LLC and The Associated Press
TORONTO, CANADA - MARCH 23: Anton Khudobin #35 of the Boston Bruins defends the goal during warm up prior to NHL...