The loss snapped Atlanta's four-game winning streak that brought them within a point of Boston for eighth place and the final playoff berth in the Eastern Conference.
During the second intermisson, Atlanta assistant coach Randy Cunneyworth said his team was "shooting itself in the foot" with mental errors. By the end of the game, the Thrashers were full of holes.
Boston center David Krejci opened the scoring at 9:25 of the first period when he out-worked Atlanta defenseman Zach Bogosian to a loose puck at the side of the net and beat goalie Johan Hedberg. Milan Lucic made it 2-0 midway through the second with a goal assisted by Krejci.
With three minutes left in the second period, Atlanta had an excellent chance to get back in the game when forward Colby Armstrong was awarded a penalty shot. However, Bruins goalie Tuukka Rask made a glove save on his way to a shutout.
Miroslav Satan scored with four seconds left in the second period, and Steve Begin scored less than two minutes into the third to put the game away. Bruins trade deadline acquisition Dennis Seidenberg had a big game on the blue line, finishing the game plus-2 with a team high 24 minutes of ice-time.
After the Bruins looked sharp and uninspired in a 3-0 last Thursday in the hyped-up battle against Matt Cooke and the Pittsburgh Penguins, their character was called into question. They have answered the bell with wins over the Rangers on Sunday and in Atlanta.
Boston out-shot Atlanta, 33-27. The Bruins now have a three-point lead over Atlanta and seven-point lead over the ninth-place New York Rangers, who host the rival Islanders on Wednesday.
Other than Eric Boulton's heavyweight scrap with Bruins enforcer Shawn Thornton, there was curiously little life in the Thrashers in their biggest game of the season.
"I've been in louder libraries," said Bruins television play-by-play announcer Jack Edwards.