The Capitals played one of their best periods of the postseason Tuesday night in Game 3 of the Eastern Conference semifinals against the Tampa Bay Lightning. A three-goal spurt in the second period against Dwayne Roloson gave the Caps a 3-2 lead, and for a time it seemed they might finally break out of their funk against the Bolts.

But one good period isn’t enough, not against Tampa Bay, not in these playoffs. The Bolts scored two goals 24 seconds apart early in the third period and just like that, the momentum the Capitals had worked so hard to build was gone. And it wasn’t coming back, especially after the Lightning went into a Habs-like trap to hold on to a 4-3 victory.

Now the Caps have to win here Wednesday night in Game 4 at St. Pete Times Forum, or once again the hockey season in Washington will barely outlast the cherry blossoms.

Game 3 was a must-win for the Capitals any way you looked at it — winning four straight in the playoffs is certainly not impossible, but it’s close — but losing the game the way they did added insult to injury. In the locker room afterward, the mood was reminiscent of December, when the Caps were in the midst of their eight-game losing streak and had that glazed look, unable to explain their inability to score or to do much of anything else, either.

Washington Capitals Coach Bruce Boudreau and his team now trail the Tampa Bay Lightning 3-0. (Jonathan Newton/WASHINGTON POST)

“I wish I could explain it,” Karl Alzner said of the third-period collapse.

His teammates echoed those sentiments. Marcus Johansson found several ways to say that the Capitals had to score more goals and give up fewer goals — hard to argue with that. But no one in the room seemed quite sure of what happened, which is not good when the team has less than 24 hours to fix it.

In December, they fixed the problem by changing their system, their style, and some of their personnel, all in an effort to be at their best not in January or February, but in April and beyond, because they wanted this to be the year they stayed in the playoffs past Mother’s Day, Memorial Day and all the other days of May.

Now, they’re trying to hold on through Cinco de Mayo.

“We’re a team that surprised a lot of people,” Alzner said. “We lost eight straight and came back and won the [Eastern Conference].”

That was then; this is now. They went nearly 12 minutes without a shot in the third period, uncharacteristic even in the new defensive scheme. That’s not going to get it done, not against a talented Tampa Bay team that needed seven games to dispatch Pittsburgh and is now looking and feeling invincible.

“We always come back in the third period,” Lightning Coach Guy Boucher said. “I think everything’s a habit. And we’ve made it a habit this year to believe that in third periods, we can make it happen. It’s all in the mind.”

With his team trailing 1-0 after the first period, Coach Bruce Boudreau must have had some choice words during the intermission. Less than a minute into the second, Alex Ovechkin had a breakaway chance against Roloson, who blocked his shot. But Ovechkin got the rebound to Mike Knuble, who scored. The second goal came on a shot from John Carlson near the blue line that got past two defenders and Roloson with the deception of a Livan Hernandez curveball.

Then came the Caps’ real opportunity, a 5-on-3 after hooking penalties on Tampa Bay’s Brett Clark and Adam Hall. The Caps toyed with Roloson a bit before closing in with a flurry of shots, but it was Ovechkin — assisted by Alexander Semin and Mike Green — who gave them their 3-2 lead and broke their scoreless streak on the power play in this series.

Finally, they looked like the Caps of old — or at least like the Caps of the first round, when they dismissed the Rangers in five games, not with ease, but certainly not with this much effort and angst.

“We played pretty good until the third period,” said Nicklas Backstrom, who has just two assists in the postseason. “We just gave it away.”

“I can’t put my finger on it,” Alzner said. “We got a little complacent. We wanted to play smart and protect the lead.”

It might be smart, to protect the lead, but the Capitals should never be complacent, not in the playoffs, not until they’ve shaken the reputation as a team that can’t get out of May and into June.

“It’s going to take everything we have,” Alzner said. “We have the personnel to do it.”

True. But it’s become evident in this series that so, too, do the Lightning.