TAMPA — Lightning defenseman Ryan McDonagh had heard it from coaches before the game Sunday, had preached it to teammates throughout the game: Keep Boston off the power play and you take away the Bruins' best chance to score.

That strategy had the Lightning up 2-1 with five minutes to play, but McDonagh still found himself in the one place he didn't want to be with a one-goal lead: the penalty box.

McDonagh lost his footing and fell, resorting to a tripping penalty to avoid a prime scoring opportunity for David Pastrnak and putting his trust in the Lightning penalty-kill unit.

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"I was so nervous being in there. You don't want to be in that position, to put the team in that position," McDonagh said.

In the first 30 seconds of the power play alone, the Lightning blocked three Bruins shots and Andrei Vasilevskiy saved another. Tyler Johnson went down to block a shot, losing his stick, and Ryan Callahan got a breakaway, only to pin the puck against the boards, killing off 20 seconds of power play without even attempting a shot.

Said McDonagh: "Excellent job… It was huge. It was great to see everybody step up and sacrifice."

Video: Lightning defenseman Ryan McDonagh talks about clutch penalty kill in final five minutes to close out an elimination win against Bruins. pic.twitter.com/23tJyZBc4o — Greg Auman (@gregauman) May 6, 2018

Going into the series, this was where the Lightning were most vulnerable. Tampa Bay ranked 27th in the NHL in penalty kill, and the Bruins' power play ranked fourth. Boston scored six power-play goals in their four wins against Toronto, and they'd gone 3-for-5 in the previous two games, getting their only goal Sunday again with the man advantage.

"There's no question our penalty kill has been under a microscope here this whole series," McDonagh said. "They did some damage to us, it's fair to say, and obviously in a clutch moment like that it's great to see everyone step up."

Alex Killorn, Johnson and Dan Girardi were credited with blocked shots in the penalty kill, and when Boston got the advantage again by pulling goalie Tuukka Rask, the Lightning clinched the win on Anton Stralman's empty-net goal with 1:24 left.

Video: Ryan Callahan talks about the Lightning earning much-needed rest by eliminating the Bruins in five games, as they did with New Jersey. pic.twitter.com/pWHtwwQkvo — Greg Auman (@gregauman) May 6, 2018

"Our PK guys did a heck of a job, sacrificing their bodies, and Vasilevskiy made some huge saves for us again," center Brayden Point said.

That challenge won't go away any time soon. If the Capitals advance to fly Tampa Bay, they ranked seventh in the league on power play, and if the Penguins advance, they have the league's most dangerous power play.

Contact Greg Auman at gauman@tampabay.com and (813) 310-2690. Follow @gregauman