After their two most complete performances of the season produced a pair of shutout victories over the weekend, the Bruins went back to beating themselves on Tuesday in Toronto.

The B’s single-filed their way to the penalty box in the second period and the Maple Leafs’ power play, ranked 31st in the league coming into the game, made them pay with two quick PP goals, powering the Leafs to a 4-0 victory at Scotiabank Arena. Three of the four goals came on power-plays, of which the B’s gave the Leafs a whopping seven.

The Leafs, who got a strong performance from goalie Anthony Stolarz (29 saves), gave the B’s chances, too, but the visitors went 0-for-6 on the PP. It was the B’s third shutout loss of the young season.

Toronto, playing without their star center Auston Matthews, snapped an eight-game regular season losing streak to the B’s.

The game marked the Bruin debut for Tyler Johnson, who finally signed on Monday after coming to training camp on a tryout deal. Meanwhile, the B’s created more cap space by placing Max Jones on waivers earlier in the day.

The first period was scoreless and evenly played in a relatively tight-checking opening 20 minutes.

Both teams had a couple of decent scoring chances. The Leafs just missed a couple of backdoor pass attempts on power plays while Stolarz made good stops on a Justin Brazeau deflection and a quick one-timer from Charlie Coyle on a late power play.

That power play came about when Chris Tanev drilled David Pastrnak into the boards. Brad Marchand came to his teammate’s defense, collaring the bigger Tanev and bringing him to the ice. Tanev got the double minor while Marchand just got the two.

The B’s lost defenseman Andrew Peeke earlier in the period when Max Pacioretty rammed him into the boards with a hit that was originally called a five-minute major. But after a video review, it was ruled that hit was clean. Peeke, who appeared to be favoring his shoulder area, did not return. With the organization light on righthanded defensemen, a Peeke absence for an extended period could hurt. Even on this night, his loss was a problem with the penalties the B’s would take, considering Peeke sees a lot of PK time.

Midway through the second period, the B’s parade to the box began and the Leafs scored two power-play goals in 1:14.

The B’s gave up their first goal in seven-plus periods on a Leafs’ power-play goal that should have never happened. At 5-on-5, Jeremy Swayman appeared to be ready to cover the puck without much pressure from the Leafs. But whether he fumbled the puck or he tried to move it, the loose puck surprised his teammates around him. Nikita Zadorov took down Pacioretty in front of the net and was called for interference.

Twenty-nine seconds after Zadorov took a seat, Morgan Rielly banged a blue line shot off the post and in for the 1-0 lead at 8:44.

Then Pastrnak, benched on Sunday for sloppy play, took an offensive zone high-sticking penalty off a faceoff, and William Nylander scored a fortunate goal on the PP, banking a centering pass off Brandon Carlo and in.

After Stolarz robbed Brazeau on a 3-on-1, Charlie McAvoy took another offensive zone penalty. The B’s killed that off, but it was their third penalty in 2:14.

To his credit, Pastrnak drew two Toronto penalties later in the second but they could not convert on either of them, the second of which was truncated by a Marchand offensive zone penalty.

The B’s pressured early in the third but couldn’t beat Stolarz. And after Mark Kastelic took a bad roughing penalty, Matthew Knies scored on a deflection.

Coach Jim Montgomery pulled Swayman for an extra skater with over four minutes to go, but seconds after he made his way to the bench, Steven Lorentz buried it into the empty net.