Going on the power play shouldn’t become a defensive liability.

Boston coach Bruce Cassidy had mixed feelings about his power play following the Bruins 4-1 victory over the Columbus Blue Jackets in Game 4 of their Eastern Conference semifinal on Thursday night at Nationwide Arena. The Bruins evened the series at 2-2 with Game 5 on Saturday night at the TD Garden.

The Bruins had only one power-play goal in the first three games. That came on a wobbly shot from the left point by defenseman Matt Grzelcyk in the first period of Game 2 at the Garden.

The Bruins scored twice on the power play in Game 4 with center Patrice Bergeron on the business end of both. But over the course of Boston’s six power-play situations, the Bruins gave up many odd-man rushes in the opposite direction that required yeoman efforts by goalie Tuukka Rask to neutralize.

“We’ve seen a little bit this year and played through those stretches and I think we gave up 15 shorties,” said Cassidy. “Part of that is personnel when you have four forwards that have some risk in their game.

“I’m not saying I love that part of it but they also scored a couple of goals so there is some give and take there. You got to trust them to play the right way.”

Cassidy believes the Bruins’ problems keeping the Blue Jackets hemmed in their zone originated along the blue line. Cassidy reconfigured his first unit during the game when he removed David Pastrnak from the right point and replaced him with center David Krejci.

Cassidy realigned the Bruins first unit with Bergeron between Brad Marchand and Jake DeBrusk with defenseman Torey Krug on left point.

“I don’t like when we mismanage pucks at the blue line high, we’ve got be harder at keeping them alive,” said Cassidy. “That was a bit of a message to Pasta there on one and you are going to have mistakes.

“Torey and March got crisscrossed and all of a sudden the puck’s going the other way. I don’t know what happened, I can’t see down in that corner but those ones happen.

“But when you can dig in a little harder to keep a puck alive, maybe put it in your skates or hammer down the boards.”

Cassidy did not conduct practice on Friday but a few players were at Warrior Ice Arena in Brighton for various reasons. Krejci, who logged 5:59 of power play ice time, acknowledged the problem and the need to correct it going forward.

“That shouldn’t happen,” said Krejci. “We are going to look at some video and correct those mistakes because that shouldn’t be happening. “Once in a while, but I think they had more than two off-man rushes on our power play and that can’t happen.”

The Bruins’ penalty kill was the contributing factor in their 3-2 double overtime loss in Game 3. The Blue Jackets scored a pair of power-play goals that included the game winner by Matt Duchene. The Bruins killed off four Columbus power plays in Game 4.

“The PK was a lot better than in the last couple of games,” said right wing Noel Acciari. “We were able to shut down their power play and they are playing well.”