Coming out of the gate on fire, the Bruins did manage to tie the game early, but gave up two power play goals late in the period to fall into a 4-2 deficit heading into the third period.
Milan Lucic picked up the goal for the Bruins just 18 seconds into the second period, taking a nifty feed from David Krejci and putting it past Brent Johnson for his 25th goal of the year.
The ice seemed to be tilted for the Bruins until a couple of penalties put the Bruins down 5-on-3 for 1:52.
The Penguins capitalized on both of the penalties, including goals from James Neal and another from Sidney Crosby with just over a minute to go in the period.
The first penalty was against Daniel Paille who was called for charging after knocking Matt Niskanen into the boards. Rich Peverley followed eight seconds later, getting called for a high stick.
And as if that wasn't enough, Andrew Ference decided he had enough of Neal and dropped his gloves with him, just before Crosby scored.
The Bruins head into the final 20 minutes with Ference out for the first couple of minutes due to his fight, and with two goals to make up.