Danault lay on the ice for several minutes before being taken away on a stretcher.
He was moving and appeared to be speaking to medical staff before he left the ice, to an ovation from the Bell Centre crowd.
Chara, who has one of the hardest shots in the National Hockey League, looked on in concern as trainers attended to Danault.
The game was halted for intermission after Danault was injured, and the extra 1:37 was added to the start of the third period.
Nicolas Deslauriers answered back for Montreal just 2:50 later off of an unassisted wrister, while Alex Galchenyuk ripped one home on the power play at 8:51 to give the Canadiens a 3-2 lead.
Canadiens coach Claude Julien said after the game that Danault would remain in hospital overnight and would be re-evaluated on Sunday.
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As to what caused the outage, in the first place, it would seem that it was due to condensation following heavy rainfall. Power in the South Hall was restored within minutes, and power has now been fully restored to all areas.
Brad Marchand scored the game-winner for Boston when he snuck a wrist shot through Carey Price's five-hole after Price stopped 29 of 32 shots in regulation and overtime.
He has seven goals and 15 assists in 43 games this season.
The Canadiens issued a statement during the third period that said: "Danault suffered a head injury". Danault was carried off the ice on the gurney and taken by ambulance to hospital for observation. "He is awake and moving". It was his 11th of the season and the 100th of his career.
Specialty items: While Galchenyuk scored a power-play goal, the Canadiens failed to take advantage of their opportunities with the extra man.
But the Bruins tied it again with 2:18 left in the second.
The Bruins will resume play on Monday, with the team set to host the Dallas Stars at TD Garden for a 1 p.m. matchup.