The Bruins’ enforcer was in a fight two seconds after puck dropped in the first period, then added goals in the second and third to reach seven for the first time in his career.
Patrice Bergeron had a goal and two assists for Boston, which had lost three of four and needed the win before heading out on a five-game road trip next week.
Tim Thomas stopped 26 shots and improved to 16-4-3.
Dustin Byfuglien scored his 13th goal of the season for the Thrashers, who will host the rematch with the Bruins in a week. The way this one ended, both teams will be geared up for the next meeting — or round — after a melee that broke out with 4:06 left to play and resulted in 96 penalty minutes.
Thornton wasn’t on the ice for this one, but Andrew Ference was and jumped Atlanta’s Freddy Meyer after he took out Milan Lucic with a high hit. Ference left his gloves behind as he charged Meyer for a quick fight that sparked several others that left Ference with blood dripping from his right eye as he was led from the ice.
Only the goalies sat out the fracas as all 10 skaters on the ice went at it. Lucic was one of the first escorted off after landing a shot on Meyer when the players had packed together in between fights. Five players received game misconducts and Lucic was called for a match penalty.
Before that, fans had been chanting “We want Thornton” to celebrate the latest version of a Big Bad Bruin and his offensive outburst.
Michael Ryder made it 2-0 Boston with a wrist shot off an assist from Bergeron with 15:56 left in the third, then 56 seconds later Thornton tied his career high with his sixth goal of the season.
Adam McQuaid dug the puck out of the corner and backhanded it to Thornton for a one-timer from the slot.
Thornton looked like a natural scorer again with 15:06 left in the game when he skated in alone, faked to his backhand and flipped the puck over sprawled out Atlanta goalie Ondrej Pavelec.
The puck had barely hit the ice on the opening faceoff before it was joined by two pair of gloves as Thornton and Eric Boulton of Atlanta got in a fight just 2 seconds into the game. Thornton and Boulton exchanged swings for more than a minute before the linesmen separated them.
Boston outshot Atlanta 36-27. … The Bruins’ five-game road trip starts Monday at Florida. … Bergeron’s goal with 17:00 left in the first period snapped a scoreless streak of 105 minutes, 57 seconds for the Bruins.