“Guys are comfortable and confident and that’s what you want going into Game 7,” veteran Mike Knuble said of the Capitals, who must win in Boston to advance. (Ricky Carioti/The Washington Post)

As the Washington Capitals sat in the dressing room at their Arlington practice facility ahead of a flight to Boston for one final showdown with the Bruins in this Eastern Conference quarterfinal series, the mood was noticeably loose.

Players lobbed well-intended jabs at each other, exchanged jokes with reporters and genuinely seemed relaxed to the point that an uninformed observer might not have believed the same team will be fighting to keep its season alive Wednesday night in Game 7 at TD Garden.

There’s no reason to be anything but calm, the Capitals said. Most of them have been here before — facing a game that will ultimately determine the success or failure of everything they’ve accomplished up to this point. Even those with minimal playoff experience endured an often unpredictable, sometimes tense 2011-12 season that tested the group’s ability to come together and find an identity within a defensive system under the guidance of a rookie NHL head coach.

While the Capitals certainly haven’t followed any script that was laid out for them, they are one win away from advancing to the second round past the defending Stanley Cup champions. All that remains is to trust in each other and the system for what should be another tight game.

“We’re content with where we are. It’s kind of who we are,” veteran Mike Knuble said. “And so I’m excited to go, excited to get it underway. Guys are comfortable and confident and that’s what you want going into Game 7. You look around the room and know that everybody’s going to be in this game and everybody’s going to show up.”

Since they returned to the playoffs in 2008, the Capitals have gone 1-3 in Game 7s. Washington lost to Philadelphia in 2008; defeated the Rangers in the first round only to fall to Pittsburgh in seven in 2009; and lost to Montreal in 2010. Seven players remain on the roster from that series against the Flyers four years ago, but only five — Alex Ovechkin, Alexander Semin, Nicklas Backstrom, Mike Green and Brooks Laich — played in each Game 7.

Washington’s postseason disappointments weren’t limited to those ultimate do-or-die contests, as several younger players realized the disappointing sting of elimination when the team was swept by Tampa Bay in the second round in 2011.

“We’ve learned from [the previous exits],” said defenseman Jeff Schultz, who is expected to be back in the lineup for Game 7. “We know when we get to the last five minutes of the game to be calm out there if we’re holding a lead or need a goal. Guys know not to get too jacked up.”

There are undeniable differences between this year’s team and those previous incarnations, though, from the addition of new players to the presence of Coach Dale Hunter and the defense-first mind-set he brought to a group that was accustomed to run-and-gun.

Learning how to adhere to Hunter’s style of play was an arduous process. Throughout the regular season Washington would play cohesively one night, only to be plagued by dysfunction and deviation from the plan the next.

By the time they scraped their way into the postseason, however, the Capitals were grounded in their game. Washington has been at its most consistent under Hunter in this series. The violent swings in the team’s ability to execute that dotted the regular season are all but absent, and it has allowed the Capitals to weather the emotional flux of the playoffs with relative ease.

“I think everybody feels better,” Backstrom said. “Everybody’s working for each other and that’s what you’ve gotta do if you keep doing like this I think we’ll win tomorrow — or we’ll have a good chance.”

Said Troy Brouwer, “When we’ve been getting down a goal or two goals, we’re staying composed.”

The Capitals’ ability to remain poised and unflinching in their dedication to the type of play that helped them reach this point will be what holds the most sway over their fortunes in Game 7 against the Bruins. So there’s really no point in getting uptight — might as well enjoy the ride.

“It’s good. I mean, there’s no point in having nerves right now,” rookie goalie Braden Holtby said. “This is fun. This is what we’re hoping for. We’re still the underdogs here. We’re going into Boston, and I know we like that energy in our dressing room right now, and we’re gonna use that to our advantage.”