You couldn’t erase the looks of pleasure and relief that swept across the faces of the Capitals this week. They’d finally gotten to enjoy a laugher, stomping the sad Edmonton Oilers, 5-0, for their sixth straight win.

“I can’t remember [us] scoring five goals in a game,” said Alex Ovechkin after his two highlight-reel goals and an assist that gave him 600 career points. “Our power play finally worked. . . . Is kind of a big night.”

Is kind of an understatement?

Just two weeks ago, after the Caps lost 6-0 to the New York Rangers to drop their record to 32-20-10, they heard home ice boos; then, not many in the NHL would’ve picked the Caps to go deep into the Stanley Cup playoffs.

What’s wrong with Ovechkin? Will Coach Bruce Boudreau be fired? What’s General Manager George McPhee going to do at the trade deadline? How could the Caps fall from the top-scoring team in the NHL last year (by 45 goals), to a club not in the top 20? And the power play: from No. 1 to No. 25 in a year?

Capitals left wing Alex Ovechkin on his way to scoring his 2nd goal of the night aginst Edmonton, (Jonathan Newton/WASHINGTON POST)

All that seems changed. For now. Since McPhee added three key players at the trade deadline, the Caps haven’t lost. We’ll see how long it lasts.

“I hope it’s about 47 more games,” said Boudreau, who appears to have added the 14 games left in the regular season, plus enough to play for a Cup.

Depending on the month, the Caps are one of hockey’s most talented teams with a bright future or they are one of the more overrated and in need of an overhaul. Right now, they’re clicking. Has the light gone on — the light in their heads and hearts, not the just the red light behind the goal?

“We’re [finally] playing like I thought we would,” said team owner Ted Leonsis. “We thought we might take a little step backwards because we got a little younger with so many rookies. Now we’ve added veterans. We’re getting healthier. That’s why I feel good.”

The Caps agree on the moment their season changed from frustration, self-doubt and criticism to a sense that luck’s their 21st man. McPhee’s most important deadline addition was Jason Arnott, 36, a 6-foot-5 center with 900 career points and his name on the Stanley Cup; a bruiser with skills.

With this reshaped team, the Caps were 48 seconds from losing again on March 1. One goal down against the Islanders, Boudreau pulled his goalie. Arnott battled for a puck in the corner, then threaded a pass to Brooks Laich for the game-tying goal.

“The clutch play Arnott made, a pass right on the tape to Laich,” McPhee said. “Can one play change a whole part of the season? It did. It did.”

The Caps won, 2-1, in overtime. They ripped off three more wins — each by one goal — before stomping Edmonton.

“There’s definitely turning points,” Boudreau said. “Sometimes that’s all it takes. It can ignite a great streak.”

The key to the rest of the Caps’ season is getting their old power-play efficiency back near the top of the league.

“We’ve improved in areas where we wanted to make progress — goaltending, defense and penalty kill,” McPhee said. “We’re No. 5 in goals-against. We haven’t been in the top 10 in 10 years. But the power play has to work. We have the personnel.”

Why hasn’t it? Until Wednesday, the Caps had gone 45 games without a game with more than one power-play goal. Everybody has a theory. But it remains a mystery. And it’s at the very center of the Caps’ season.

“There’s a certain rhythm to the power play. Things have to be second nature. Move the puck without thinking,” McPhee said. “We’ve been getting it and holding it too long, cradling it. That’s been the problem.

“Move it, shoot it, move it, shoot it.”

With less than a month left in the regular season, will the Caps take a huge step forward, or back?

As might be expected, the arc of the team’s year has mirrored the Great Eight’s year. And that’s probably how the last act in spring will play out, too. At midseason, Ovechkin told McPhee, “I’m trying. It’s just not happening. But it will.”

Pundits theorized that the NHL had figured out Ovechkin and that he might already have passed his peak. Even Caps executives think Ovechkin’s disappointments in the Olympics and NHL playoffs last year left his pride wounded and contributed to a poor first half of the season. But that’s changed in recent weeks, too.

“He’s the Alex we all know now,” McPhee said.

The Caps have known all year that their season would be judged by whether they peaked for the playoffs and performed best under pressure. Even two weeks ago, with three goalies age 22, 22 and 21, with two gifted but inexperienced rookie defensemen, with a crummy power play and a slumping Ovechkin, who’d have predicted the Caps would suddenly be red hot?

Maybe this season will end in premature tears, just like the last two. But that’s certainly not how it feels right now.

“Our room feels like a real nice mix of veterans and youth,” McPhee said. “I like to think we’ve done a real good job.”

Last month, who would have believed it?

By next month, will anyone doubt it?