Toronto got a pair of goals from Tyler Bozak, while teammates Jake Gardiner and James van Riemsdyk added a goal each en route to a 4-3 win. Toronto goalie Jonathan Bernier finished with 38 saves, and Maple Leafs forward Phil Kessel contributed three assists.
The Bruins' loss coupled with the Lightning's 2-1 win over the New York Rangers left Boston and Tampa Bay tied for the top spot in the Atlantic Division.
Rask has enjoyed success against the Maple Leafs and entered the game with a 9-1-0 regular-season record and a 1.42 goals-against average versus Toronto.
Boston took a 1-0 lead at 3:38 of the first period when Marchand netted his 11th goal of the season. Teammate Reilly Smith did all the grunt work on the play, carrying the puck to the net with three defenders covering him. Bernier made the initial save on Smith, but Marchand was there for the rebound and pumped it in.
Toronto tied it at 1-1 when Bozak notched his first of the game at 5:52 of the first period. Rask made the save on the initial shot, but Bozak grabbed the rebound and knocked it in for his eighth goal of the season.
The game's tempo continued to be back and forth, and midway through the first period, Bergeron gave Boston a 2-1 lead. He retrieved the puck off the back wall and quickly snuck a backhander past Bernier on the short side at 10:48. It was Bergeron's 11th goal of the season.
At 11:57 of the first, the Bruins' Carl Soderberg was called for hooking and the Maple Leafs took advantage with a power-play goal to tie it at 2-2 at 12:47. Van Riemsdyk gained control of the puck in front and made a nifty pass to Bozak, who pumped in the easy back-door shot for his second goal of the game.
Toronto scored its second power-play goal at 7:09 of the second period to gain a 3-2 lead. The Maple Leafs used quick, crisp, tape-to-tape passing to set up Gardiner's tally, which beat Rask to the glove side.
Entering the third with a one-goal advantage, the Maple Leafs added to that lead only one minute into the period. Van Riemsdyk's wrister from the right faceoff circle beat Rask to give Toronto a 4-2 lead.
Boston cut its deficit to one when Campbell scored his third of the season at 9:35. The Bruins' energy line was creating havoc on the forecheck when Daniel Paille collected a loose puck behind the Toronto net and made a nifty backhand, no-look pass to Campbell, who beat Bernier with a backhander.
That's all the Bruins could muster as Toronto finished with the victory.
DROP 'EM: In his first game on home ice since returning to the lineup after serving a 15-game suspension, the Bruins' Shawn Thornton dropped the gloves with the Leafs' Frazer McLaren at 3:03 of the first period. As Thornton skated to the penalty box after the bout, the fans gave him a standing ovation. It was Thornton's sixth fighting major of the season. The Bruins entered the game with a 50-22-10 record when Thornton records a fighting major.
MOMENT OF SILENCE: Prior to the game, the Bruins held a moment of silence for Sam Berns, who passed away last Friday due to complications from progeria, a rare genetic condition that produces rapid aging in children. He was 17. Earlier this season, Berns attended a Bruins game and was an honorary equipment manager.
UP NEXT: The Bruins return to the road and travel to Dallas to face the Stars on Thursday. Boston then travels to Chicago for a Stanley Cup rematch against the Blackhawks at 12:30 Sunday afternoon.