Every seven-game series, no matter the sport, has a rhythm. In some cases the matchups are so lopsided that sweeps are not only possible, but inevitable. In others, the teams are well-matched and in those cases, each game takes on a different significance.

And then there’s the case of the Capitals, who seem to let every series go seven games, who are occasionally snakebit, occasionally passive, and often, at the end of it all, left shaking their heads. So despite the fact that the team with the best record in the Eastern Conference this season leads the Rangers, two games to one, in their quarterfinal series, Sunday’s Game 3 loss seems to have everyone a tad . . . tense.

This may seem like an overreaction — it’s just one loss, after all — but this is what happens when you build the playoff history the Caps have put together in the past few seasons. And it now makes Game 4 a crucial one — perhaps even a must-win game for the Capitals. According to the Elias Sports Bureau, teams that win Game 4 of a best-of-seven series go on to win their series 78 percent of the time.

The gap between a 3-1 series lead and a 2-2 series tie is just one game, mathematically, but mentally that gap looks like the Grand Canyon. “Definitely,” Matt Hendricks said Tuesday after the Caps finished a short practice at Kettler Ice Complex.

“If you look at it, going 2-2 turns it into the best of three; if we go up 3-1 we’re going back home for Game 5 and the series is really in our favor.”

Of course, Hendricks wasn’t here last season, when the Caps blew a 3-1 lead against Montreal. But although he hasn’t been scarred by the Caps’ recent postseason disappointments, he and the rest of his teammates know the value of avoiding a seven-game series at all costs.

“Any series you want to get done as quick as possible,” Jason Chimera said. “If you could win in four every series it would be great, it would be the best situation ever. You want to get some rest for some guys. We’ve got to put the hammer down on Wednesday and keep on going from there.”

Chimera is right; a sweep would have been great for everyone, including America’s most tightly wound fan base. But a sweep was never going to happen against the Rangers, and anyone who thought otherwise was kidding themselves. A lot of analysis was made about how the Rangers weren’t the ideal first-round opponent for the Capitals, and that’s probably true. The teams are very similar in some regards, although the Caps’ offensive talent is superior.

But everyone needs to get over the idea that there is an ideal first-round opponent for the Capitals. In fact, forget the Rangers; the Caps are largely competing with themselves and their recent wretched playoff history. That is their first-round opponent. That is what they have to beat.

And that’s why Game 4 is likely a must-win game. Coming home and needing one win in three games is the best possible position to be in. Yes, they’ve been in it before, and failed. That’s why they need to pry that King Kong-size monkey off their backs once and for all.

They are so close to redemption. They are playing postseason-style hockey. Their goaltender, Michal Neuvirth, is consistent and “calm as a cucumber,” as Coach Bruce Boudreau put it. They added players at the trade deadline who are helping on and off the ice (although they will welcome the eventual return of Dennis Wideman).

But in Game 3 there was a lack of the pounding energy we saw in Games 1 and 2. The Rangers, on the other hand, played like a team down 2-0. They were all over the ice. They were able to goad the Caps into some silly penalties, which handcuffed the Caps’ offense. The Rangers were able to impede — and sometimes interfere with — Neuvirth. And their winning goal — bouncing off two Caps — was fluky. Still counts as a goal, though.

“They were a desperate hockey team and we didn’t match their work ethic and their enthusiasm,” Matt Bradley said. “There’s really no excuse for it, but it was one game. It’s not like we played a bad game, we just didn’t play as well as well as we needed to. We’ll be ready for Wednesday.”

They’ll need to be. They get help from the schedule: There were two days off between Games 3 and 4 and there will be another two between 4 and 5 — extra time for treatment, extra time to prepare, extra time to practice. Unfortunately, that extra time also gives the Caps time to think — about how they’ve been in this position before, and how that worked out for them. The best cure for that: Try to put this series to bed quickly, and that won’t happen without a win in Game 4.