TAMPA — When Nikita Kucherov barreled in on Braden Holtby as the first period slipped away, making a ridiculous on-his-back move and scoring a building-rattling goal, the temptation was there to damn the Washington Capitals and the luck they still carry around, even here, in the Eastern Conference finals for the first time in two decades. They had played 19 minutes 50 seconds of solid, admirable, playoff-worthy hockey. They held a one-goal lead. And with one long pass and one electric move, it had slipped away.

Except here’s the thing about these Capitals, this group that is now guaranteed to be playing at least into the third weekend in May: The old standards about their luck and their fortitude no longer apply. Lock them in a cabinet. Keep them in a scrapbook. Don’t tell your kids what it once was like to root for this team.

Yes, it’s only one exchange, and Friday was only one game, and we don’t know what will happen to them the rest of this series against the Tampa Bay Lightning. But we know the Capitals have a thorough 4-2 victory in the opener, and we know it was built on an exchange the likes of which the Capitals have never seen so deep in the postseason.

“Obviously,” Holtby said, “a turning point in the game.”

Distilled, it was this: The Lightning scored the tying goal. The referees (rightly) took it away. The Capitals scored two seconds later. It’s essentially first-and-goal from the 1 — and Washington returned an interception 99 yards.

“The crowd was kind of stunned a little bit,” defenseman John Carlson said.

Zero in on that moment because it not only was the most important of Game 1, but it means something about what’s happening in these Stanley Cup playoffs. After Amalie Arena erupted following Kucherov’s piece of brilliance, the four officials skated to mid-ice, conferred briefly — and announced the Lightning had too many men on the ice. Replays showed the call was indisputable — one, two, three, four, five . . . and Kucherov made six.

The goal was wiped out. With 7.1 seconds remaining in the period, the Capitals went on the power play. They had a faceoff in the Tampa Bay zone. Carlson and forward T.J. Oshie talked about asking the officials to put some more time on the clock, “to give ourselves 10 or 11 or 12 seconds,” Carlson said.

Oshie won the draw. And then — boom! — Alex Ovechkin blasted one home.

That’s a game flipping like a fish pulled onto the dock, in a two-second span.

“Any time you score even in the last minute of a period, it can be deflating to the team that gets scored on,” Oshie said, “because you have to come in here and watch the clock for 15 minutes and think about that goal that just went in that you wish you would have prevented.”

The Capitals played such a complete game — or at least a complete first two periods — that almost no aspect should go without mention. Their power play clearly presents a threat to Tampa Bay, which had the fourth-worst penalty kill during the season. Washington, too, can now play stifling defense, a quality that won it the clincher in the last round against Pittsburgh and an area of their game that befuddled the Lightning in the opener of this round.

When the Capitals scored their third goal less than three minutes into the second period, Tampa Bay had only three shots. When the Capitals scored their fourth goal four minutes later, Tampa Bay had just four shots. As Holtby continued to look calm, the Caps drove his counterpart, Vezina Trophy finalist Andrei Vasilevskiy, to the bench after two periods.

And Washington did all this without playmaking center Nicklas Backstrom, out with a hand injury. Could they be even better when No. 19 returns?

Maybe, maybe not. Either way, what it seems like is that, whatever happens, the Capitals will control so much of their fate.

This team has spoken all season about how it isn’t haunted by everything that has made springtime so miserable so frequently in the District. That all sounds like lip service — until there’s some proof.

Well, now there’s proof — and more. Beating Pittsburgh was important and symbolic and exhilarating — for the team and the town. But what we’re finding on the other side of that victory — a victory that got Ovechkin past the second round for the first time — is a professional group that isn’t going to wait for a bounce to go its way. Instead, these Capitals will force their own bounces and be happy when someone else provides them with something fortuitous.

“We just realize,” Ovechkin said, “we just have to play our way.”

Maybe playing that way — and believing in it — creates their own fortune.

The fortuitous development Friday was Tampa Bay’s own error. Think about past playoffs and the lens through which we viewed them. In those instances, it would have been Ovechkin barreling down the ice, scoring a crazy goal, celebrating as the horn sounded — only to look up the ice and watch as it was waved off for some silly reason. There would have been memes about the Capitals learning to count, perhaps with help from “Sesame Street” characters. We would have made it a piece of the puzzle to fit in with all those old debacles.

Not now. On Friday night, it was Kucherov of Tampa Bay, not Ovechkin of Washington, who had the goal disallowed. It was the Lightning, not the Capitals, that had to deal with its own paralyzing mistake.

And more importantly, it was the Capitals who looked like they didn’t need the help. They will take the odd bounce, sure. But what is developing now is some evidence that they’re good enough to win in all manner of ways, fortune be damned.