Back in September, hockey experts predicted that the Washington Capitals would sit atop the Eastern Conference in the spring. This year, they would advance beyond the second round of the playoffs. Some pundits even picked them to vie for the Stanley Cup. Since those prognostications came in, though, not much has gone according to plan.

Washington kicks off its first-round playoff series Thursday at the Boston Bruins after an arduous year in which its coach was fired, systems were altered, star players underachieved and injuries abounded. Forget the Stanley Cup — a mere playoff berth was in doubt until the penultimate game of the regular season.

Perhaps pinning the same hopes and expectations that existed heading into this season on this team — the one that survived the 2011-12 campaign rather than dominated it — isn’t realistic or fair as the Washington faces the defending Stanley Cup champion Bruins, who are an intimidating foe by any measure. But don’t tell the Capitals that.

They might have gone off script, and they may be considered underdogs in the first round for the first time in at least four seasons, but that doesn’t mean they have any intention of settling.

“First round isn’t a success. Second, third round is not. The Cup is success,” defenseman Karl Alzner said flatly. “The third round would be getting closer to success, but a lot of the same guys have been here for a while — at least the same core of guys, and those guys are all fed up with bowing out after the first, second round. It doesn’t matter if the team is at the top of the league or finishing in eighth; it’s all the same. There’s no success for any of us unless we win.”

This spring marks Washington’s fifth consecutive postseason appearance, but it’s the first time the team has entered as a lower seed in that stretch and the first time since 2008 it hasn’t finished among the top two seeds in the East.

The Bruins are the ones who occupy the role of heavy favorites — and understandably so, even if Alex Ovechkin disagrees with the labeling.

“I don’t think somebody can say who’s favorite [and] who’s not, it’s the playoffs,” the Capitals’ star left wing said. “Last couple years everybody thought we gonna be undefeated and it’s going to be easy for us in the playoffs. We lost. It’s situation right now, we don’t have to listen to [reporters], to fans, what they say. We just have to concentrate and this group of guys have to be together for long time.”

Boston’s advantage on paper stems from having the bulk of its championship roster return from a season ago. The Bruins boast the same depth that wore down opponents and helped win three seven-game series in 2011. Not to mention that reigning Vezina and Conn Smythe winner Tim Thomas will man the Bruins’ net, while unproven rookie Braden Holtby will make his first NHL postseason appearance for Washington.

To clinch the seventh seed, the Capitals won five of their final seven regular season contests with their most consistent hockey to date under Coach Dale Hunter. In this matchup against a confident Boston squad, they’ll need more of that composed all-around game.

Washington will also need to match the physicality of their foe, which didn’t earn the “Big, Bad Bruins” moniker for being polite on the ice. Boston likes to wreak havoc on opposing goaltenders and to finish bone-crunching checks. The Bruins won’t pass up an opportunity to intimidate the Capitals.

“Pound for pound, we don’t have the size to match up with every guy in their lineup, but if we play physical as a team we can wear teams out,” said forward Matt Hendricks, who also emphasized the Capitals’ need for discipline within their own systems. “We’re going to have to be physical with them.

“We can’t be individual against these guys. That’s when they can eat you up because their defensive play is so strong,” Hendricks added. “It can’t be one group of defensemen and one group of forwards playing the right system — it has to be every line doing it. So no matter what happens . . . you’re going to be able to go out and play and not deviate from what the coaches want us to do.”

As formidable an opponent as Boston is, though, upsets are far from rare in the Stanley Cup playoffs. And if there’s any team familiar with them it’s the Capitals, who have been knocked off in each of the past four seasons by lower-seeded teams.

In the six seasons since the lockout, first-round upsets — defined simply as a lower seed defeating a higher seed — have occurred in 18 out of 48 series, or 37.5 percent. Only five of those upsets were an eighth- or seventh-place team claiming a first-round win, though.

But that, after all, is why they play the games. The Capitals know anything is possible. After an unpredictable season, perhaps the playoffs won’t go quite as anyone envisions, either.

“A lot of years there’s so much pressure on us, and I think now it’s been a little up and down this season,” center Nicklas Backstrom said. “We just made it into the playoff, and we’re excited to play in the playoff and obviously it’s a tough matchup against Boston. We haven’t played our best hockey yet, and hopefully we can do that now.”