Frustration was the main ingredient of a recipe that came with a sour taste for the Bruins on Thursday night, as Jim Montgomery’s squad blew a two-goal lead in the third period and fell to the Kings in a 3-2 shootout at TD Garden.

“I sensed frustration, to be honest,” Montgomery said of where things went wrong for the Bruins in this one. “I think our first period was OK, I thought our second period started off really well and we started doing a lot of really good things. And then when we got up 2-0, we got away from those things that were giving us success.

“I thought tonight we took a lot of retaliatory penalties. That usually is some sort of frustration involved, whether it’s the game — you know, in the first period [there were] eight minutes of special teams — so there’s a lot of guys not getting the minutes that they’re used to. So it creeps into your game and you’re waiting for things to get going and you’re not getting in the flow of the game as you usually do.”

Up 2-0 through two periods of play, the Bruins’ third period was just miss after miss, and the Bruins’ final-frame trouble became too much to overcome when the Bruins found themselves trying to kill off 1:53 of a 5-on-3 advantage for the Kings with less than four minutes remaining in the third period and with Boston clinging to a one-goal edge.

That, after the Bruins whiffed on a power-play chance that would’ve allowed them to jump out to a two-goal lead and by all means put the Kings to bed, was a pain the Bruins saw coming from a mile away.

“I actually said it to [Bruins assistant coach] Chris Kelly on the bench,” Montgomery admitted. “[I said], ‘If we don’t score in the second power play that we got. We’re going to end up in a tied ballgame.'”

Montgomery nailed it before it happened, too, as the Kings found their break during the 5-on-3 sequence when Adrian Kempe scored his second goal of the game through a sliding, splitting Linus Ullmark with 2:10 left in the game.

And when the Bruins failed to convert on another power-play opportunity, this one with less than a minute left in regulation and bleeding over into the overtime frame, the Bruins simply continued to dig their own grave.

The shootout, which was ended by a goal from the Kings’ Trevor Moore in the bottom of the seventh round, marked the first time that the Bruins had suffered a loss in a game that saw them ahead through two periods of play.

And it really did throw a huge damper on what looked like a promising night for the B’s.

Scoreless through 20 minutes of action, a delayed penalty was all that was needed for the B’s to strike first, as Matt Grzelcyk fed Taylor Hall with enough time and space for a straight-up rip through the Kings’ Pheonix Copley.

The goal, which came at the 7:53 mark of the middle frame, pushed Hall’s recent hot run up to seven goals and 14 points over his last 14 games, and was the 40th goal Hall has scored with the Bruins since his 2021 move from Buffalo to Boston.

Not to be outdone, Brad Marchand decided to match Hall’s absolute rocket with one of his own, this time on the power play, and just 2:09 after Hall’s game-opening marker.

In goal, Bruins netminder Linus Ullmark was perfect until the 50th minute of action when the Kings’ Adrian Kempe tucked home a deficit-slicing goal to put the Kings on the board on their 22nd shot of the evening.

It would be one of just two blemishes on the night for Ullmark, who finished with 28 saves in the losing effort, and stopped four of LA’s six shooters prior to Moore’s game-winning shootout goal.

Copley, meanwhile, was brilliant for the Kings, and finished with 33 saves in the win.

On a lineup front, Bruins center David Krejci returned to the lineup after missing the previous two games with a lower-body injury. Krejci’s return put the veteran pivot back in the middle of Pavel Zacha and David Pastrnak on the Black and Gold’s second line, while Jake DeBrusk moved back up to the first line with Patrice Bergeron and Brad Marchand.

With Krejci back, Craig Smith sat as a healthy scratch for the Bruins.

B’s defenseman Hampus Lindholm, who was originally considered a game-time decision due to an illness, suited up for this game and finished with one shot and one block in 22 minutes of time on ice.

“I thought he seemed to be even better than good enough,” Montgomery said of Lindholm.

The Bruins will continue this homestand with a Saturday matinee against the Blue Jackets.