PITTSBURGH — They were 18 seconds that changed Game 2 and perhaps this first-round series.

With the Rangers trailing by a goal against a formidable Penguins team that had added star center Evgeni Malkin from the injured list for the game, and down one game to none in the first-round playoff series, things looked bleak for the Blueshirts on Saturday at a boisterous CONSOL Energy Center.

StorySkjei and McIlrath contribute to playoff win StoryBrassard sweats out review of breakaway goal StoryLundqvist rises to the occasion

But Keith Yandle and Derick Brassard scored at 12:38 and 12:56 of the second period to swing the momentum toward the Rangers, who won, 4-2, and tied the series in a tough game that increased in physicality after that turning point.

Yandle’s tying goal came on the first of J.T. Miller’s three assists in the period, and Brassard (two assists) scored when he deftly stayed onside after Miller’s bouncing headman pass and beat goalie Jeff Zatkoff high on a breakaway. Penguins coach Mike Sullivan challenged the goal, saying Brassard was offside, but after a review, the goal counted.

“We got a fortunate bounce on the second one and the first one is a play we do all the time,” Miller said, “pucks and bodies to the net. But when you get the opportunity, you’ve got to finish. If we did that in Game 1 at the beginning, it’s a different game.”

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The Rangers didn’t drop into a shell and Mats Zuccarello extended the lead to 3-1 at 16:52 on a sharp cross-ice pass from Miller. Just 39 seconds into the third period, Chris Kreider made it 4-1. He blocked a clearing attempt deep in the Penguins’ zone and snapped a shot past Zatkoff, starting his second consecutive game in place of the injured Marc-Andre Fleury.

“Our intensity and battle level was much higher than the first game [Wednesday night’s 5-2 loss],” Marc Staal said. “We were much stronger in the middle of the ice, limited the opportunities and allowed Hank to see the shots.”

Henrik Lundqvist, returning from an injury near his right eye that forced him out of Game 1, was sharp early and made 29 saves, including two on the doorstep in the final minute. Zat koff, who was pulled for an extra skater with 2:45 to play, had 24.

So now the series moves to Madison Square Garden, where the Rangers were 27-10-4, for Games 3 and 4 on Tuesday and Thursday nights. The win guaranteed a return to Pittsburgh for Game 5.

“Tonight was a good start,” Stepan said, “but after an hour or so we move on, because now it’s a five-game series. ’’

Both Penguins goals came on the power play. Phil Kessel scored his second on a four-on-three as the Penguins closed to 4-2 with 14:18 left in regulation.

From the start through the last of the 57 hits — the Penguins had 25 — the Rangers decided not to go down without a fight.

“Committing to a physical game and finishing our checks makes it harder [for the other team] in a seven-game series,” Kreider said.

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“We were finally able to capitalize on a few of our looks,” coach Alan Vigneault said. “I felt we needed to execute better with the puck, and when you get an opportunity to play the body, you have to play the body.”

Five Rangers had at least six hits.

It was a fierce third period, punctuated by a slash by Chris Kunitz on Marc Staal. Kevin Klein saw it and immediately fought Kunitz with 8:17 to play.

“It’s good to push back and stick up for your teammates, but at the same time, you have to be responsible,” Miller said. “You have to play whistle-to- whistle and try not to worry about the stuff after the whistle.”

As the temperature rises in this series, that might not be easy.