This time, the Toronto Maple Leafs had no comeback.

On so many occasions in the regular season, the Maple Leafs could turn on a tap and allow their ample speed and skill to flow and beat the opposition.

But that approach doesn't usually work in the Stanley Cup playoffs, a time when games are tighter and strong positional play is the order of the day. The team that limits its mistakes usually prevails.

The Maple Leafs made a boatload of blunders and as a result, they find themselves behind 1-0 in their opening-round series after a 5-1 drubbing by the Boston Bruins at TD Garden on Thursday.

Let's start with Nazem Kadri. The 27-year-old Toronto centre has done so much growing up in the past three seasons, on and off the ice. It wasn't long ago that Maple Leafs president Brendan Shanahan suspended Kadri for an undisclosed off-ice incident in March 2015.

For the most part, he turned the corner after that. Head coach Mike Babcock was a big help, shaping Kadri into a strong checking centre who has delivered back-to-back 32-goal seasons.

But just like the super pest on the other side, Boston's Brad Marchand, has his relapses, Kadri stumbled back to his old, undisciplined ways in Game 1.

He likely will be suspended for his final transgression of the evening, a reckless boarding penalty on Bruins fourth-line forward Tommy Wingels midway through the third period.

Sure, Wingels deserved a two-minute penalty when he placed his elbow firmly in the face of Maple Leafs forward Mitch Marner. But down 4-1, Kadri snapped and took a run at a defenceless Wingels. A five-minute major for boarding and a 10-minute misconduct sent the badly behaved Kadri to the dressing room for the night as did a shaken Wingels.

Now how long will Kadri be suspended for? One game or two?

"I just felt like he made contact with Mitchy's head to start and I didn't see a call there," Kadri said afterward. "[Wingels] was turning up the wall so I was committed to the hit.

"I certainly wasn't trying to hit him when he was down like that."

In any event, Kadri has some apologizing to do to his teammates. With the game still 3-1 and a comeback still possible because of the Maple Leafs' talent, Kadri first took a run at Wingels from behind early in the third period.

The Bruins, who already had scored twice on the power play, didn't increase their lead with Kadri in the penalty box. But they did score less than a minute after he exited.

The Maple Leafs forward didn't agree with the boarding penalty and that anger was still evident four minutes later in the second incident against Wingels. The Bruins piled on with their third goal with the man-advantage.

Boston was the better team, especially in the first 10 minutes of the game, late in the second and in the entire third period.

The Maple Leafs had their moments on the power play, too. But they lacked finish.

The difference was in the final five minutes of the second period with the game tied 1-1. David Backes banged in the go-ahead goal on the power play after the Leafs' penalty-killing unit had been caught on the ice for more than a 100 seconds and an exhausted Toronto defenceman Ron Hainsey could not out-muscle Backes in front.

A few shifts later, Tomas Plekanec and the Maple Leafs' fourth line was caught on the ice against the Bruins top line. As a result, David Pastrnak buried a critical goal from the high slot with 38 ticks left on the clock.

"We'll let the league do what the league does," Toronto coach Mike Babcock said when asked about a possible suspension for Kadri. "The bottom line is that you have to be disciplined at all times. Emotion is real important in a game, but it has to be controlled.

"We have a day to solve our problems."