Where have the Bruins we saw all season gone?

David Pastrnak was shut down by the Blue Jackets on Tuesday night.MATTHEW J. LEE/GLOBE STAFF/Globe Staff

COLUMBUS, Ohio — It all looked so right at the start of the third period. So familiar, so hopeful.

The three big-name Bruins took the ice to open the final period of this pivotal playoff game like they were getting the old gang back together, a trio of Patrice Bergeron, Brad Marchand, and David Pastrnak that has propelled the Bruins to so much success this season, and one, the visiting team hoped, could break the Bruins out of a nightlong funk.

It all looked so good, with the struggling Pastrnak rejoining his mates on the top line, moving up from the third line where he started the night.

It all made so much sense.

At least in theory.

But turning the theoretical into reality requires duplicating what wrote that theory in the first place. Unfortunately, the Bruins who took the ice Tuesday night in Columbus barely resemble the ones who earned the second-best record in the conference by season’s end. The top-line reunion that started the third period ultimately did nothing to feed the flicker of hope that ended the second, when a Jake DeBrusk goal at :40 pulled the Bruins within one of high-flying Columbus, in but one small example of what was missing on the Boston bench.

An ineffective power play, officially 0 for 2 on the night. One even less-effective penalty kill, leading to the winning goal. An alarming lack of physicality, reflected in getting outhit, 53-28. A frustrating paucity of goals, only two in the last five periods of regulation and two overtimes. Put it all together and you begin to understand how a 2-1 loss to Columbus doesn’t feel nearly as close as the score indicates, and how a 2-1 series deficit in this second-round clash with the Blue Jackets can understandably leave you wondering: Where have the Bruins we saw all season gone?

“I think the only thing that’d be a little different is the final execution part,” fourth-line forward Sean Kuraly said. “We hit a couple posts. The chances are there. We’ve just got to keep getting to the net, keep shooting, keep in front of [Columbus goaltender Sergei Bobrovsky]. A lot of the stuff we did in the regular season is happening in a lot of parts of the game.”

Well, except for a successful power play. The Bruins couldn’t capitalize on their one full one Tuesday and saw their second, which came late in the third period and felt like a perfect opportunity to tie the game, disappear after a measly 16 seconds, when Bergeron was whistled for tripping. Or a good penalty kill, when one exceptionally bad effort in the second period left goaltender Tuukka Rask under interminable siege, the goal he gave up to Matt Duchene with seven seconds left in the man-advantage a reflection not on his inability to stop the puck but on his teammates’ inability to clear it.

“They’re tight games. Five on five, it’s tight. There’s not much given on both sides,” Bergeron said. “So yeah, it’s real important [to play better on special teams]. It’s a bit of the story again tonight.

“I think they’re putting the puck on net, that’s what they’re doing right now, converging and getting there and once the puck gets there there’s rebounds and opens up the other play. They’re doing a good job of that. We have to go back to being stingier and getting more clears. It starts there. When we do we’re in good shape.”

Blue Jackets goaltender Sergei Bobrovsky makes one of his 36 saves Tuesday in Game 3.Matthew J. Lee/Globe staff/Globe Staff

No doubt, the credit on Tuesday night goes to the Blue Jackets as much as blame goes on the Bruins. Bobrovsky was a near-impenetrable wall, and the rest of the Columbus roster plays this Torts-inspired brand of physical, hard-charging, shot-blocking hockey that is a credit to what John Tortorella has long espoused from behind his bench. But that doesn’t change how disconcerting it is to watch the Bruins play this way, to see them fail to connect on passes, unable to clear on penalty kills, to back away from physical contact. Imagine the Patriots taking their usual high seed into the playoffs and suddenly turning into the Jaguars, or the Steelers, or the Jets, making enough mistakes of their own that the opponent doesn’t even have to. It just doesn’t look right.

The Bruins would be wise to figure it out by Thursday night and Game 4, because the thought of returning here with the season on the line is scary. This isn’t an easy place to win. The novelty of hosting its first second-round playoff game in franchise history is not lost on the hometown crowd, and their delirium only underscored the engineered noise in this building. Cannon fire (no, really), overhead sirens, and an occasional drum section were backed by the fans’ repeated chants of “C-B-J,” while a mini-blimp floated among the rafters dropping packages, T-shirts came flying out of launching guns, and strobing blue lights danced around the arena.

Who could think in that mess?

“We just need to take a deep breath, kind of regroup, maybe watch the mistakes that we made and go from there,” defenseman Brandon Carlo said.

The Bruins aren’t dead, not by any means. A win Thursday and the home-ice advantage is back on track. That’s the mind-set Bruce Cassidy is counting on, making sure to point out Tuesday that “they’ve all been close games. You could make an argument every one could have gone either way. We did enough to win. We were in attack mode from the get-go as opposed to weathering the storm.”

That wasn’t enough against the more forceful Blue Jackets. “They’re a heavy team, we know that,” Cassidy said. “We like to think we are, when we’re at our best.”

But the Bruins weren’t at their best Tuesday. Far from it.