So much has been so predictable in these playoffs. A sloppy, scoreless first period in Thursday night’s Game 4 between the Rangers and Bruins seemed to be more of the same from what the Blueshirts had shown in this series.

But after two-plus wild and crazy periods, the offense was no longer as harmless as cotton candy and the power play temporarily ended its long-running joke.

The flipped script only could be written — ending with the Rangers’ 4-3 overtime win at Madison Square Garden — because of the pillars that seem to stand strong just about every second.

Henrik Lundqvist was once again the constant that can’t be talked about enough, making 37 saves and saving the season once again, but defenseman Ryan McDonagh’s play was equally important, after logging a team-high 29:43, leading a depleted defense and assisting on the game-winning goal.

With Anton Stralman out with an injury suffered in Game 3 and Marc Staal still out with an eye injury, McDonagh had three blocked shots and two hits, while providing stellar defensive pressure and aggression on offense to create several scoring chances.

“He’s done it all year long,” center Derek Stepan said. “It’s nothing different. It’s the playoffs and the [defense] is going to have to continue to log big minutes.”

McDonagh has carried over the dominant defense from helping keep Alex Ovechkin scoreless in the final six games of the opening round, but his offensive awareness has elevated a Rangers offense headed to the obituaries.