WASHINGTON — From period to period this season, the Rangers have seemed like vastly different teams. The structure crumbles after a good defensive or offensive 20 or 30 minutes.

That again was the case in the 5-2 loss to the NHL-leading Capitals on Sunday. The Blueshirts allowed two early power-play goals and Justin Williams’ hat trick at even strength as they failed in another bid to string two victories together. They haven’t accomplished that since Nov. 21-23 and concluded a three-game road trip 1-2.

“Special teams is a huge part of the game, but every play is a big play,” defenseman Dan Girardi said. “All these small plays that we’ve been doing for the last couple years, it just feels like we’ve been getting away from ourselves. In the past when we make a mistake, I feel like we get out of there, it’s not killing us . . . Now one mistake turns into two or three. No one’s pointing fingers, but we’ve got to string some wins together here.”

Leading 3-2 after 40 minutes at Verizon Center, where they have won 12 straight games, the Capitals put this one away early in the third. J.T. Miller, along the boards in his own zone, flung an unnecessary pass into the middle that was intercepted. Williams, alone in front, easily buried his second goal of the game past Antti Raanta, playing his first game in a month, to extend the lead to 4-2 with 4:51 gone.

Williams completed his hat trick into an empty net at 18:09 when his long wrister bounced in off Derick Brassard’s skate.

“I don’t think we were giving them an overly amount of chances,” Marc Staal said, noting the Capitals had 24 shots, “but the one chance they’re getting, it’s a backdoor tap-in or a play where we don’t give our goalie a chance to block it.”

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After a solid defensive effort by the Rangers (24-16-5, 53 points) in the first period, the Capitals scored two goals in a span of 1:02 in the second period to take a 3-1 lead.

Chris Kreider scored the opening goal at 10:17, but the Capitals (34-8-3, 71 points) scored the next three, two on the power play by Alex Ovechkin and Marcus Johansson. The Blueshirts lost their way, leaving the Capitals open often, and seemed a step behind.

The Rangers have allowed 12 power-play goals in the last 11 games.

“It’s been probably the most frustrating thing, the penalty-killing,” Ryan McDonagh said. “That’s been a strong suit of us for as long as I can remember. For some reason, we’re letting the opposition dictate the plays, the pace. We’re trying to get all four guys on the same page. We’ve got to figure it out because it’s changing momentum of games, like in Philadelphia, and in this game, it gave them a lot of life.”

After Kreider scored his second goal and third in the past two games to cut the lead to 3-2, Capitals goaltender Braden Holtby went to the dressing room and was replaced by backup Phillip Grubauer with 2:18 left in the second period. The team said Holtby was suffering from dehydration. But the Rangers, playing their third game in four days, couldn’t dent Grubauer as the Capitals won their third in a row against the Blueshirts.

“We need guys to make a handful of plays,” McDonagh said. “It’s a fine line for us right now.”