Hoffman and Brassard scored just 25 seconds apart in the first period and exploited a depleted Boston defense to give Ottawa an early 2-0 lead. "I knew if I stuck with it, I'd get a chance eventually".
Cassidy expects to match Miller with John-Michael Liles on Boston's third defensive pairing for Wednesday night's game, which is set for 7:30 p.m. ET at the Garden.
The assist was the second of the game for Karlsson while Ryan scored his second goal of the series, as the Senators captured their second straight OT victory.
The sellout crowd of 22,175 booed as the final seconds of the second period ticked off, and there were more jeers in the third.
Ottawa goaltender Craig Anderson made a great glove save off a tough shot by Kevan Miller.
It was MacArthur's first goal since April 19, 2015, as he has missed all but 13 games since then while sidelined with concussion issues. We were 20 minutes away from being up 2-0. "But it's too bad we fell short".
The Sens now lead the series 2-1 after Monday night's 4-3 overtime win in Boston.
Defenceman Marc Methot isn't letting the Ottawa Senators' Game 2 win against the Boston Bruins get to his head.
"During the season if he was getting pulled or whatever he showed up the next day and did the work and I think we're really proud of him the way he's playing right now, but at the same time you could have swore he played the exact same way the whole year", Perron said. "And then [Monday night] I thought they did".
In Game 2, Ottawa was fortunate enough to convert on two of their shots from outside the home plate area.
What will decide Wednesday night's game?
With the series now reaching critical mass time for the Bruins, they need to find a way to keep Karlsson from wheeling and dealing, from jump-starting the Senators offensively and take him out of his comfort zone.
The fans were already in fine form before the teams hit the ice, whooping it up when the maniacal laugh of Ozzy Osbourne erupted from the PA system, signalling the start of heavy metal anthem Crazy Train.
The three goals were scored on just seven shots in the period, the Bruins with just 10 through two.
The pass by Karlsson was a thing of beauty and he had to flip it over top of 6-foot-9 Zdeno Chara to put it on the tape of Hoffman's stick at the Boston blueline.
Asked what his team needs to do in Game 4, Boston winger Brad Marchand, a 39-goal scorer in the regular season who scored the Game 1 victor before being blanked in the next two, said, "Definitely a better start".
Not long after Hoffman gave the Senators what should have been a comfortable lead with 16:18 left in the second on the power play, the Bruins cued the comeback with two goals in a span of 37 seconds. The Bruins sent D Matt Grzelcyk back to AHL Providence during the game.
With all this, Boston looked to be riding high into the third with all the momentum and an Ottawa team that was just defeated and broken looking.
The Bruins' blue line is depleted with injuries. Sure, it was a blast by Phaneuf for his first career OT winning goal that kept the club from falling into a 2-0 hole in the series, but Alex Burrows did a tremendous job screening Rask in front.