By Matt Kalman, CBS Boston

BOSTON (CBS) – Now we know the limits of Bruins coach Bruce Cassidy’s magic powers.

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Game after game the Bruins lost defensemen to injury, yet they kept on winning.

That run ended with a 4-3 overtime loss at Ottawa in Game 2 of the Eastern Conference first round series on Saturday. The series is now tied 1-1 after the Bruins lost a 3-1 lead in the third period.

Instead of the Bruins’ depleted defense corps earning all the accolades, it was the Senators’ defensemen who turned around the game and shifted the momentum of the series.

Chris Wideman scored on his only shot of the game to cut the Boston lead to 3-2. Erik Karlsson took a tour of the offensive zone before setting up Derick Brassard’s game-tying goal with an almost impossible cross-ice pass. And then 1:59 into overtime Dion Phaneuf hammered a one-timer past Tuukka Rask for the game-winner with, ironically, three Bruins defensemen on the ice (Zdeno Chara had just exited the penalty box).

What in the name of Shane Hnidy and Wade Redden are the Bruins going to do if they don’t get healthy for Game 3? If they don’t have anyone back, they can insert Matt Grzelcyk or Tommy Cross and hope they can duplicate the way they played through the first five periods of this series on Monday.

Even with Torey Krug, Brandon Carlo and Colin Miller (not to mention center David Krejci) sidelined, Boston’s strong defensive play carried over from Game 1 on Saturday and everyone in the group was involved, even after Adam McQuaid left in the first period with an upper-body injury. No. 9 defenseman Joe Morrow, playing his first NHL game since Jan. 22, took a hit to help a clean break-in progress before Drew Stafford’s goal made it 1-0. Also on the play, Chara retrieved the puck behind the Ottawa net after John-Michael Liles, after taking Morrow’s place on the ice, aggressively fired a shot from the high slot.

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Charlie McAvoy looked as poised as ever, despite having to play on the top pair with Chara, and was instrumental in the Bruins going ahead 3-1 on Patrice Bergeron’s power-play goal. All the Bruins’ defensemen were playing well in their own and, more importantly, making passes to help the Bruins bust the Senators’ neutral-zone trap. Most of Ottawa’s top forwards were left off the stat sheet, especially at 5-on-5.

But five periods were all Cinderella had to enjoy the ball. Playing with five defensemen for the fourth straight game clearly caught up to the Bruins. Ottawa coach Guy Boucher must have also lit a fire under some of his best players. Derick Brassard had been shot-less until he scored on one of three shots in the third period. Kyle Turris became more aggressive, and Zack Smith, Mark Stone and Mike Hoffman formed a new line that was a threat every time it was on the ice.

Smith helped lure McAvoy in front of Rask on Wideman’s goal. Everyone got caught puck watching on Karlsson’s set up of Brassard. With 12.5 seconds remaining in the third, Chara flipped the puck over the glass without any pressure on him. The Senators went on the power play, which carried over into overtime. They hit the post twice and Phaneuf had a great shot that Rask stopped but couldn’t keep in his glove just before the defenseman’s winning goal.

Rask could’ve been better over the final 21:59 but he made some sensational saves in the first two periods and the dangerousness of Ottawa’s scoring chances went through the roof in the third period. The Bruins could’ve benefited from a line other than Bergeron’s or Dominic Moore’s making the Senators work in their own end. But for the Bruins to execute their game plan, they need defensemen and although there were five healthy bodies in skates and sweaters, the injuries finally caught up to them. The Bruins have played with five defensemen for 80 percent of their past four games.

And with McQuaid out and Chara in the box, the Bruins were left to kill a penalty with Miller, Morrow and Liles. Ottawa should be ashamed it didn’t score until after the penalty expired.

Now we know what it takes for the sit-back-and-wait Senators to get going offensively. If the Bruins lose a couple more defenseman maybe Ottawa will start to resemble the ‘80s Oilers. We also now know the limits of Cassidy’s tutelage. No NHL team ever makes injuries an excuse, but the Bruins deserve to blame their poor healthy for their plight.

All they can really do now is hope they get a defenseman or two back in the lineup for Game 3 or they may not survive the upcoming week.

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Matt Kalman covers the Bruins for and also contributes to and several other media outlets. Follow him on Twitter @TheBruinsBlog.