The Washington Capitals had scored less than a minute earlier when a referee lifted his arm and a whistle sounded, and a collective groan echoed through Capital One Arena. Center Evgeny Kuznetsov skated to the penalty box with slumped shoulders, and soon the team’s penalty kill would fail again. Arizona’s Alex ­Galchenyuk was left all alone in front of the net, and though goaltender Braden Holtby stopped his first shot, the center swatted in his own rebound.

The Coyotes celebrated, and the Capitals left the ice deflated, still looking for answers when playing shorthanded. Against an Arizona team that was playing its second game in less than 24 hours, Washington hurt itself with three ­offensive-zone penalties, and an ­ineffective penalty kill cost the Capitals for the second straight game. They allowed one of the league’s worst power plays to score twice in their 4-1 loss.

The Capitals have allowed six power-play goals in their past four games.

“It’s not getting it done,” Coach Todd Reirden said. “You can continue to look at it different ways. We have some different personnel in that situation, a different way of going about things on the penalty kill, but right now it’s costing us games. We can’t expect to win when you’re giving up penalty-kill goals like we are at the rate we are right now.”

Washington (7-6-3) was stingier at even strength during this five-game homestand, but the shorthanded unit has become the team’s biggest concern. The Capitals have allowed two power-play goals in five of their 16 games. Meanwhile, the offense has dried up, managing just four goals in the past three contests. Arizona’s Darcy Kuemper made 38 saves a day after a 4-0 loss at Pittsburgh.

“Just that little extra seems to be lacking,” said Capitals defenseman John Carlson, who returned to the lineup after missing Friday’s loss to Columbus. “Just call it a little blah. We’re just a little blah right now. We’re used to trusting ourselves to make some plays that right now aren’t happening, so maybe it’s time to pivot back to a little more simpler game and build up that execution point. Just over-passing a little bit when we shouldn’t be, and when we need to make passes, they’re just a little off.”

After Washington yielded two man-advantage goals in Friday’s 2-1 loss to the Blue Jackets, the team devoted the second half of Saturday’s practice to working on its penalty kill. That unit was middle-of-the-pack last season, ranking 15th in the NHL with an 80.3 percent rate of success, and Reirden identified shorthanded play as an area he could improve with new assistant coach Scott Arniel. The unit is missing injured defenseman Brooks Orpik and suspended winger Tom Wilson, and it’s now among the league’s bottom five.

After 15 minutes of slow-moving hockey, the Capitals had an extended shift in the Coyotes’ zone for the first time, but defenseman Matt Niskanen was whistled for tripping, Washington’s second infraction of the frame. The Coyotes entered the game with seven power-play goals, tied for the fewest in the NHL, but they were able to take advantage with four seconds left on Niskanen’s penalty.

Reirden wants to be more aggressive on the penalty kill, but late in the opportunity, T.J. Oshie, Nicklas Backstrom and Carlson all sped down the ice for a shorthanded chance, leaving just Dmitry Orlov back. Kuemper saved Carlson’s shot, and then the Coyotes had an odd-man rush barreling back toward Holtby. Vinnie Hinostroza finished off a tic-tac-toe passing play to lift Arizona to a 1-0 lead 16:56 into the game.

“It’s just a bad read by us,” Backstrom said. “Too many guys attacking there instead of maybe playing it out and waiting for it to be five-on-five. We saw an opportunity. It’s easy to say that after, too. But, yeah, there’s absolutely an area that we can be better at.”

The Coyotes made it a two-goal lead 11:57 into the second period when the Capitals’ fourth line overpassed on an odd-man rush, leading to a turnover. Arizona’s Richard Panik had a partial breakaway and beat Holtby to the glove side.

Looking for a spark before the game, Reirden reunited a proven trio in captain Alex Ovechkin, Backstrom and Oshie. Those three once were one of the best lines in hockey, but they haven’t played a full game side by side since the 2016-17 season.

That was Washington’s one bright spot in this game. With the Capitals down 2-0, Ovechkin set up a wide-open Backstrom in the right faceoff circle for Washington’s first goal of the game at 12:41 of the second period. But in what has become a pattern, a penalty killed the momentum: Less than a minute later, Kuznetsov was called for high-sticking Arizona’s Jason Demers, and the Coyotes restored their two-goal lead with Galchenyuk’s goal.

“That’s something that can ease some of the burden on our penalty kill as we’re going through a struggling time with that right now. Not to be shorthanded is the best way to solve that,” Reirden said. “It’s one of the areas we have to clean up, too . . . especially in the offensive zone.”

Derek Stepan sealed the win in the third period with an empty-net goal.

The Capitals collected five of a possible 10 points during this homestand, and they will now embark on a four-game trip starting Tuesday to Minnesota, Winnipeg, Colorado and Montreal.

“Right now, if we keep playing like this,” Backstrom said, “we’re not going to get any points.”

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