After sneaking back into the playoffs for the first time in three seasons, Boston had a first-round matchup with the Ottawa Senators, who swept Boston in their regular-season series.
Despite the regular-season struggles against Ottawa, the Bruins were favored by many to come out on top.
That didn't happen, as the Senators took the series in six games. Let's take a look at some reasons why.
In case there was any doubt, Erik Karlsson is an absolute machine.
It's no shock that the Senators defenseman (and leading Norris candidate) was the team's most influential player. What is surprising, however, is that he was so effective while playing the entire series with two hairline fractures in his left foot.
Despite the injury, which Karlsson disclosed following the decisive Game 6, he averaged 30 minutes of ice time per game. He also racked up six assists in the series.
Karlsson was also a possession beast for much of the series and the Senators were a much different (and worse) team without him on the ice.
Numbers don't tell the whole story, though. Karlsson was also a vocal leader on the ice and took charge when the rest of his teammates occasionally strayed from the gameplan.
It can't really be overstated how depleted the Bruins were by the end of this series.
Heading into the playoffs, they were already without two key members of their blue line in Torey Krug, their best defenseman during the regular season, and Brandon Carlo, a standout rookie paired with Zdeno Chara on the top defensive pair.
Then, the Bruins lost top-six centerman David Krejci for three games, defenseman Adam McQuaid for four, and yet another defenseman, Colin Miller, for two.
As a result, the Bruins had to rely on several players who spent a the majority of the season either in depth roles, in the AHL or -- in the case of Charlie McAvoy -- playing college hockey.
Eleven Boston players made their playoff debut this season. In the Bruins Game 6 lineup, eight of the bottom-nine forwards had spent time on the team's fourth line this season. That's not ideal for an elimination game.
They were depleted and inexperienced and that took a major toll.
Following the worst regular season of his career, veteran Senators forward Bobby Ryan flipped a switch in the postseason.
Ryan had seven points in six games and led all players in the series with four goals -- two of which were game-winners.
He shot 25 percent and six of those seven points came on the power play, so I'd venture to say that level of production isn't particularly sustainable as the Sens move on. Still, a series like this could do a lot for his confidence.
Without his offensive contributions in this series, it could have gone differently for the Senators.
The Bruins likely wouldn't have made the playoffs if it weren't for Brad Marchand's 39 goals and 85 points in the regular season. He was one of the better wingers in all of hockey, so respect where respect is due.
But, with that in mind, Marchand carried lofty expectations into the playoffs. He didn't necessarily play poorly -- his strong two-way game tends to drive play towards the attacking end of the ice -- but his production wasn't fantastic.
Marchand scored just one goal while adding three assists. He shot 5.6 percent while the Bruins' other key winger, David Pastrnak, struggled to hit the net for a good portion of the series.
Boston probably relies on Marchand a bit too much to carry the offense, so it really hurt them that he wasn't able to find the back of the net more over these six games.
Maybe it was coaching, maybe it was nerves and inexperience, or maybe it was a mixture, but the Bruins made far too many mistakes in this series. They led all teams with 26 minor penalties in the first round, with a lot of them coming on unforced errors. There's not a lot of room for that in the playoffs.
They also didn't get much help from the officiating, which was very poor and seemed to bite Boston through much of the series. But while that was out of the Bruins' control, their own mistakes were not.
Over the six-game series, Boston committed a couple of costly 'too many men' penalties and an absolutely mind-blowing six over-the-glass delay of game penalties -- three of which came in the first period of Game 6.
While the Bruins' strong penalty-killing unit was able to limit the damage, taking those penalties forced them to expend crucial time and energy trying to escape a hole they dug for themselves.
When you're in an elimination game like Game 6, you don't want key guys like Patrice Bergeron and Brad Marchand out there chasing the puck to kill penalties early in a game. You want them driving and attacking and putting the pressure on all game long.
Unfortunately, the Bruins spent far too much time in the box, and two of the Senators' three overtime winners -- including the series-clincher in Game 6 -- came on the power play.
Bruins accomplish plenty in tumultuous season
The Boston Bruins returned to the Stanley Cup Playoffs for the first time since 2014 and were hit with a rash of injuries before and during their Eastern Conference First Round series loss to the Ottawa Senators.
Although the Bruins were disappointed after a 3-2 overtime loss to the Senators in Game 6 at TD Garden on Sunday, Boston understood it had accomplished a lot.
"Adversity is something that you have to stick with, you have to keep fighting, keep battling," Bruins center Patrice Bergeron said. "I thought we showed a lot of character to get back in games and you know we didn't make it easy on ourselves by any means.
"But at the same time, very proud of everyone. A lot of guys came in the lineup with not much experience and were asked to play a different role and they did it. It was impressive to see that and it was next man up every time. And I think it was a great experience for the young guys for sure."
It was a tumultuous run back to the playoffs for the Bruins, who fired coach Claude Julien on Feb. 7 and replaced him with Bruce Cassidy, who had been in his first season as an assistant with Boston. The Bruins were 26-23-6 during the regular season under Julien, in his 10th season with Boston and having won the Stanley Cup in 2011. The Bruins lost their last two games under Julien and turned it around under Cassidy.
Boston went 11-3-0 following the coaching change but were 0-4-0 in its next four games. With the failures of the prior two seasons hanging over them, the Bruins responded with a six-game winning streak and a berth in the playoffs.
The adversity of the regular season prepared the Bruins to handle what was ahead. Defenseman Torey Krug sustained a lower-body injury in the 81st game of the season and never returned. Defenseman Brandon Carlo (upper body) was injured in the last game of the season and also didn't play again. In Game 1 against Ottawa, Boston lost defenseman Colin Miller, who returned from his lower-body injury for Game 4. But Adam McQuaid never returned from the lower-body injury he sustained in Game 2.
Center David Krejci warmed up for Game 1 but wasn't able to play until Game 3. Then in Game 5, he sustained a lower-body injury and didn't play in Game 6.
"Yeah, it's part of hockey, you know. We can't be really standing here and kind of feeling sorry for ourselves because we lost so many guys," Bruins captain Zdeno Chara said. "But you know that's part of the playoffs. ... But very proud of how we battled, how we never gave up. We came back multiple times every game almost, and it's fun to play when you know that there's that never-give-up attitude. Everybody did whatever it took to get that extra push, extra goal."
Every game between the Bruins and Senators was decided by one goal and four went to overtime. That's invaluable experience for younger players.
Forward David Pastrnak, who had a career-high 70 points (34 goals, 36 assists), had never appeared in the NHL postseason before. He had two goals and two assists in the series. Defenseman Charlie McAvoy, a first-round pick (No. 14) in the 2016 NHL Draft, had never played in the NHL before he averaged 26:11 of ice time and had three assists during the six-game series.
Although the Bruins still relied on veterans like Chara, Bergeron and Brad Marchand, they got a glimpse of their future.
"Yeah, I think they have a lot to build from," Bergeron said. "You know we talked about how it's a different game in the postseason and I think we've all realized it. ... I think for the young guys it's definitely a great experience and something you can't buy and I know it's going to go a long way for next year."
The Bruins have decisions to make about Cassidy's future behind the bench and about their personnel. But they made strides in the right direction this season.
The Bruins describe the end of their season, remain optimistic for the future
The Boston Bruins are out of the playoffs after falling 3-2 to the Senators in overtime at TD Garden on Sunday. And despite battling to the end in a tightly contested six-game series, players couldn’t mask their disappointment speaking afterward.
Still, several players echoed optimism regarding the team’s future.
“This team’s only going to get better and tighter and get on the right side of these one-goal games, and still be playing into rounds two, three and the finals,” said David Backes.