Hoffman's second goal of the game came midway through the second period care of a massive slapshot from the point on the power play but that's when things started to unwind for the Senators who appeared to take their foot off the gas allowing the Bruins to erase their 3-0 lead after 40 minutes.
With the power play winding down, Ottawa's Kyle Turris slid a pass to Bobby Ryan for a tap in goal to give the Senators the walk-off win. Ottawa added another goal early in the second before Boston produced a dramatic comeback.
Clarke MacArthur, Chris Wideman and Derick Brassard also scored for Ottawa.
Methot described the plane ride to Boston following Saturday's win - a come-from-behind 4-3 overtime thriller that evened the best-of-seven series at a game apiece - as "pretty calm".
Washington led 3-1 and had a chance to put the Leafs away after Kuznetsov upped the lead back to two with his first goal of the playoffs 5:39 into the second period, but Toronto's penalty-kill managed to fend off a full 2-minute 5-on-3 Capitals' power play.
Boston is hoping to get rookie rearguard Brandon Carlo and perhaps fourth line energy guy/agitator Noel Acciari back for Game 3, but it doesn't look like their best offensive defensemen, Torey Krug, will be ready. While they've outshot the Bruins, and are almost equal in shot attempts, many of those shots have come outside the home plate area (widely considered to be the danger zone), which isn't good enough when facing a goalie of Rask's calibre.
Defenseman Colin Miller is expected to play Wednesday in Boston's Game 4 matchup with the Ottawa Senators, head coach Bruce Cassidy confirmed after an optional morning skate at TD Garden.
Ottawa coach Guy Boucher, saying "rest is a weapon", kept his regulars off the ice Tuesday. "It feels great to get it for our group".
The Senators rallied from a 3-1 deficit with a two-goal third period.
BLUE JACKETS: Forward Matt Calvert was suspended by the NHL's department of player safety for Game 3 against Pittsburgh on Sunday because of his cross-check to Tom Kuhnhackl late in the third period of Game 2. Eric Karlsson and the Sens roared to life not too soon after, Karlsson had a tremendous individual shift that had Derrick Brassard wide open after drawing everyone to him, and the game was tied.
Then, just 42 seconds later, a disgusting gaffe by Ottawa's Ryan all but gift-wrapped Boston's second goal.
Game 4 is Wednesday night in Boston. Hoffman controlled the puck and easily tapped it by Rask into the right corner of the net.
The Bruins managed three shots on goal in the first and just one in the final 16:18 of the period, and neither side got off a shot in the last 9:47.
The Bruins were a decent team at home this season, going 23-17-1 in their own building.
For the second straight game, the Bruins erupted for three goals in the second to bring an anxious crowd to life.