After Sean Couturier went down with a rib injury, the Flyers’ penalty-killing units scuffled for four games. Understandably.

It’s not easy replacing the league’s best defensive forward.

But the penalty kill has regrouped, and it has played a major role in the Flyers’ four-game winning streak, the first time they have won four in a row within their first 10 games since 2008-09. The PK is 14-for-15 (93.3%) in that span after going just 8-for-14 (57.1%) in the first four games without Couturier.

“I think those guys are sacrificing and giving that 100% effort,” goalie Brian Elliott said after Sunday’s 4-3 overtime win over the Islanders. “When you do that, you tend to win some more battles, get pucks down, and [opponents] have to regroup, and that kills about 20 seconds. ... It just takes momentum away from them.”

The Flyers’ PK was 5-for-6 on Sunday, and at one point had killed 11 straight over a four-game span.

Defensemen Ivan Provorov, Phil Myers, Justin Braun, and Travis Sanheim did the heavy lifting on Sunday’s penalty kill, along with forwards Scott Laughton, Kevin Hayes, Joel Farabee, and Michael Raffl.

“We’ve been executing a lot better,” said Elliott, who made 10 shorthanded saves Sunday. “We gave up one, but all in all, I thought we did a really good job keeping things to the outside and allowing me to see ... and clearing it all the way down.”

The Flyers’ PK was 9-for-10 in the two-game sweep of the Isles.

“Our penalty killing tonight again was good,” Vigneault said after Sunday’s win. “Their goal was a shot that had eyes and found the post and then hit Moose in the back of the leg and went in. But for the most part, against a team that has tremendous amount of skill and can make plays and has some great shooters from the point, we did a great job. Our guys blocked some shots at the right time.”

While Vigneault is happy with the Flyers’ shorthanded play, he does not like the number of power-play opportunities they are allowing — 14 over the last three games.

“There is no doubt that penalty killing is part of having success. I would also say staying out of the box is something we’re going to work on,” Vigneault said. “We took way too many penalties [Sunday] and we need to get better at that.”

Especially with the Boston Bruins coming to town for a two-game series that starts Wednesday and ends Friday.

Boston’s power play was clicking at 34.9% (fifth in the NHL) entering Monday, aided by its 4-for-7 success in a recent two-game sweep of the Flyers. That power play is even more dangerous now that goal-scoring machine David Pastrnak is back in the Bruins’ lineup after recovering from offseason hip surgery.

“I know against Pittsburgh and Boston, our PK stats weren’t great,” said Hayes, whose team allowed seven goals on 15 power plays in those four contests. “But if you go back and look at the goals, there were a lot of broken plays. I mean, we have a foundation we’re supposed to stick to and, even though we gave up a goal on the penalty kill [Sunday], I thought ultimately it was the main reason why we won the game.”