The Bruins, in theory, are built on goaltending and defense. Neither was on display at the Garden on Thursday night.

Jeremy Swayman allowed a half dozen goals while the B’s defensemen could not clear the rebounds he was giving up, leading to a 6-5 loss and spoiling a Bruin comeback attempt.

With Charlie McAvoy in the box for holding, Sidney Crosby put the Penguins up 6-5 when his shot from the top of the left circle deflected off of Hampus Lindholm and through Swayman’s pads with 8:41 left in the third.

The B’s pulled Swayman with 2:41 and they had their chances to tie but just couldn’t get the equalizer.

After trailing by three goals early in the second period, the B’s clawed back to tie with two goals in the second and then a beauty of a shorthanded goal by Brad Marchand at 3:08 of the third period. Charlie Coyle bulled his wayt through the neutral zone before moving it to Marchand at the blue line for a one-on-one battle with Kris Letang. Moving to his right, Marchand made asmart stick check on Letang to get back on his forehand, move the net and then roof it over Alex Nedeljkovic to make it 5-5. It was the B’s first shorty of the year and Marchand’s second of the night.

If you like goals, this game was for you.

The first period was a wild one, and not in a good way for the Bruins or their goaltender, who gave up four goals in the opening 20 minutes.

It started with so much promise, as the B’s took the first lead of the game just 41 seconds in, with Marchand sweeping home a rebound of a David Pastrnak shot past Nedeljkovic.

But the Penguins almost immediately took control of he game and took the lead on two goals in 1:13. First, Drew O’Connor tied it up after Jeremy Swayman gave up a rebound off a Kris Letang shot.

Then coach Jim Montgomery looked to his fourth line of Johnny Beecher, Georgii Merkulov and Oskar Steen to give the team a momentum-changing shift. It didn’t work out that way. After a dominant Pittsburgh shift, Ryan Graves gave the Penguins a 2-1 lead on a deflected shot.

But just 22 seconds later, Pastrnak tied it up, taking a great Hampus Lindholm feed, throwing a fake to draw Nedeljkovic out and tucking a backhander behind him.

That, however, is where the back-and-forth ended for the period. Pittsburgh regained the lead 42 seconds after the Pastrnak on a nice looking play. Letang sent a long pass up the ice that bounced off the end and right to Sidney Crosby, who pulled it back and patiently waited for Jake Guentzel to arrive at the backdoor. Once there, Penguin captain found him for the goal.

When Lars Eller scored from bottom of the right circle at 15-58, it gave Pittsburgh the first two-goal lead of the game. At that point, wondering whether Swayman would last the game would have been fair.

It looked Swayman might be able to right himself early in the second period. But he couldn’t stop all the bleeding. On a Pittsburgh power play, he stopped Crosby on two point blank shots from the slot. But just as Brandon Carlo was getting out the penalty box, the Pens pushed the lead to three when Jeff Carter scored on another rebound goal in tight.

But with the way the game was going, the B’s still weren’t out of it, if only they could get some shots on Nedeljkovic. At 9:51, they did just that. Pastrnak made a beautiful cross-ice pass to Morgan Geekie, whose shot from the right wing – just the 12th of the game for the B’s – beat the goalie to make it 5-3.

After squandering a power play, the B’s scratched back to within a goal when Carlo’s slapper from the blue line found it’s way through Nedeljkovic with 35.8 seconds left in the period. All of a sudden, the B’s were in striking distance headed into the third.