The Toronto Maple Leafs are dead.

After the Bruins dominated in the first few games, it looked like it might be a quick opening round series for the Leafs. Ultimately, it was the only one that went all seven games. 

But, in the end, the finish line for Toronto was just more Game 7 heartbreak, once again hosted by Boston. 

Let's take a look at where things went wrong for the Maple Leafs.

Auston Matthews 

Arguably the Leafs' best player, Auston Matthews was faced with some tough matchups against a Bruins team that ranked third-best in goals allowed during the regular season.

Even still, the Leafs needed more out of him.

A prolific goal scorer and point-per-game player in the regular reason, Matthews had just two points in the series -- a goal in Game 3 and an assist in Game 5. (Toronto won both of those games.) He also finished as a minus-4 in the series.

He was completely shut down while sharing the ice with Bruins' top defenseman Zdeno Chara, and he had a tough time matching up with Boston's top line, which is one of the league's best at both ends of the ice.

He got stronger as the series went on and began generating more chances. His 27 shots matched David Pastrnak's output for the most in the series, but Pastrnak (five goals) had the finishing touch and Matthews didn't.

In the postseason, you need your best players to show up and make a significant impact, despite difficult matchups. Your best have to be better than their best. Matthews just wasn't close to good enough in this series, so the fact that the Leafs were able to force seven games despite that speaks to the quality of guys that they've got around him.

The Bruins' young offensive stars 

A pair of 21-year-old stars led the way for Boston in this series. 

The Bruins were dominant in the first couple of games, thanks in large part to the play of their top line. David Pastrnak was the standout offensively, notching four goals (including a hat trick in Game 2) and nine points through the first two contests.

That top line wasn't quite as dominant in the middle of the series and Pastrnak didn't score again until Game 7, but he did contribute two assists in a Game 5 win. His 13 points in the series are tied for most of the opening round 

This series also served as something of a coming out party for Jake Debrusk, who can now add "big game player" to his resume. Like Pastrnak, Debrusk also had five goals in the series, including two in Game 7.

He had the game-winning goal in the third period when he torched Jake Gardiner with his end-to-end speed.

Debrusk has developed into an outstanding, dynamic player for the Bruins' top six in his first season. He has a chance to become a star if he continues to be a difference-maker in the playoffs.

This Bruins team has relied on youth to supplement its veteran core all year. If there was any question about whether Boston's young stars would be debilitated by lack of postseason experience, that question was answered…at least in the first round.

Issues on the Leafs' blue line

The blue line was the biggest concern for Toronto heading into this series. Most of those concerns surrounded their questionable right side – one that is led by a 37-year-old Ron Hainsey, then Nikita Zaitsev.

The Leafs looked overmatched in the first couple of games and the defense couldn't help stop the bleeding as the Bruins dominated possession. It looked like it was going to be a quick series.

But, to their credit, Toronto eventually tightened things up on the back end and games started to get closer and closer.

Ultimately, they just couldn't keep it together in the final game, and their undoing on the defensive end came from somewhat of a surprising spot: Jake Gardiner.

Gardiner, who is the Leafs' de facto No. 1 defenseman, had a miserable Game 7 in Boston. He was on the ice for five of the Bruins' seven goals in that do-or-die finale, and he was the guy who got roasted on Debrusk's game-winner in the third period.

Not exactly the best spot to have your worst performance of the series. To Gardiner's credit, he owned up to that.

The Leafs are a good, exciting young team, but they've got to improve on the defensive end if a serious Cup run is to be in their future. It's easier said that done (top shutdown guys usually don't quickly appear out of no where) but they're just not there yet.

Goaltending

Goaltending wasn't particularly great for either team in this series. Both starters were very good at points, and very leaky at others. That's sort of been the story for them all year long. Tuukka Rask had an .899 save percentage. Frederik Andersen finished at .896.

However, with the Bruins' edge in possession, they had a better chance at overcoming inconsistent goaltending. The Leafs needed Andersen to be great to be able to stay in games. At points, he was…and they ended up winning. The problem is, he didn't have enough of those great performances.

In the games they won, Andersen had a save percentage of .950. In the games they lost, he stopped just .867 percent of what the Bruins put on net. That's a massive gap, and it's not one the Leafs could overcome.

He let in a lot of stoppable pucks, but the biggest came on Debrusk's game-winner in Game 7. That's a stop you just have to make in a big spot with the series on the line. He couldn't get it done.

Boston's resilience

Anyone who has kept tabs on the Bruins this year knows that this is a group that has been great at weathering the storm. They overcame a number of significant injuries to finish with the second-best record in the Eastern Conference. They won plenty of games that they really had no business winning.

Resilience and character are two intangibles that every Stanley Cup contender needs, and this Bruins team appears to have them both. Game 7 was a pretty clear example of that, as Boston was significantly outplayed during the second period and things looked pretty bleak when they headed into the final intermission down by a goal.

But they bounced back -- as they have so many times this year-- and found new life in a quick equalizer, then never looked back. This is a team that usually doesn't fold when things look to be stacked against them, and it's a big reason they're moving on to the second round.