BOSTON — This time around, the Boston Bruins were the ones who looked like playoff neophytes.

They looked jittery at times, especially some young players. They turned the puck over in high danger areas. They allowed breakaway after breakaway in a disastrous second period. They passed when they should have shot much of the night. And, no, the Bruins did not get the timely save when they needed it, but they also allowed far more Grade A chances than any team who thinks of itself as elite ever should.

All of that led to a total flip of the script from last year’s first-round series against these same Toronto Maple Leafs and a 4-1 loss in Game 1 at TD Garden. Now, after the Bruins battled through a brutal, injury-filled 82-game season to somehow win home-ice advantage against these Leafs once more, they handed it right back to them in one game.

A year ago, the Leafs left Boston after the first two games of the series with the look of a shell-shocked team. The Bruins had outscored the Maple Leafs 12-4, and the top line of Patrice Bergeron, Brad Marchand and David Pastrnak did just about whatever they wanted to when they crossed over the Toronto blue line.

Well, it appears these Leafs learned a thing or two from that experience, committing themselves to a brand of team defense that had seemed foreign to Toronto in the four regular-season games the Bruins played against the Leafs.

Mitch Marner (two goals) was the night’s No. 1 star, while goalie Frederik Andersen was good but didn’t have to be much better than that as the Bruins never got their offense going, from their top line on down.

“We talked a lot about taking care of the blue lines and playing playoff hockey, and lot of that wasn’t done tonight,” said Bergeron, whose line finished a minus-2 while being matched up most of the night against the Zach Hyman-John Tavares-Mitch-Marner line, as well as the Jake Muzzin-Nikita Zaitsev defense pairing. “Too many turnovers. And when that happens, you don’t really establish your forecheck or get any rhythm out of it.”

The Bruins looked like they might be off to the races once again when the took a 1-0 first-period lead on the power play (of course), on a great backdoor pass from Marchand to Bergeron. Shortly after that, Danton Heinen had a glorious chance all alone in the middle of the slot but tried an ill-advised pass that never got to its destination. That would be a recurring theme.

The Leafs tied the game on Marner’s first goal late in the first period. Then in the second period, the old bugaboo of the short-handed goal against came back to haunt the Bruins. They gave up a league-leading 15 short-handed goals in the regular season.

Jake DeBrusk could not control a bouncing puck near the Leafs’ blue line, and that was all the speedy Marner needed to see. He took off on a breakaway and was tripped from behind by DeBrusk.

“Yeah, it wasn’t fun causing the turnover there. I was just trying to get back and make a play. Obviously, I didn’t like the result of that and then he scored. I think that was the turning point of the game,” said DeBrusk.

On the penalty shot, Marner took it tantalizingly close to Tuukka Rask’s stick before pulling it back and tucking it by his left pad.

“That was a (Pastrnak) move. He’s done that in practice,” said Rask. “I put all my weight on my right foot and then I just couldn’t get there. It was a nice move.”

Rask stopped a Tavares breakaway and then another odd-man rush at the end of the second period. But he could not come up with the save on a breakaway by William Nylander. Prior to that, Matt Grzelcyk moved in on a two-on-one and appeared to have a path to the net. Grzelcyk tried a pass that never got there. The Leafs quickly transitioned, with Nazem Kadri making a great pass to spring Nylander, whose shot jumped over Rask’s stick and between his pads for a 3-1 lead.

“I got him where I wanted and I felt it hit my stick, but I guess it was a bad saver selection because it went through. I was tracking it to the corner and it ended up in the back of the net,” said Rask.

While a save on either one of those might have changed the game, Coach Bruce Cassidy didn’t blame his goalie.

“Listen, you want your goalie to stop everything,” said Cassidy. “Breakaways, breakdowns. I’m not going to put any of this on Tuukka. I’ll state the obvious. Yeah, we would have liked the penalty shot save. It might be a different game. It’s their best player, in my estimation, (scoring) a goal. Plenty of time to come back after that. Power play, (Charlie) Coyle hits the post, maybe it’s a different game (if he scores). Then we give up the next breakaway. That was on us as a team. We’ve been exposed by them on those breakaways. You give away two, three in a row that period, so shame on us.”

Now they’ll have to live with that shame until Saturday night, when they’ll encounter an opponent brimming with confidence.