Robertson cut it to 3-2 at 7:57 of the second period, redirecting a shot from Korczak for his team-leading seventh goal.
Zacha scored again, extending the lead to 4-2 at 14:24 with a wrist shot off a pass from Peterka on a 2-on-1.
"When we're playing the right way as lines, I think we find ways," Zacha said. "I think we have a lot of skill but I think when we can kind of add winning the battles and making the wall plays, that's how we scored some goals, good wall plays. And we have a fast team through the neutral zone, so we know we can use that. Just using guys for their skill sets, and I think every line can score, which is great."
Geekie pushed it to 5-2 on a breakaway at 16:57, taking a pass from Hampus Lindholm during a Pittsburgh line change to go in alone for a wrist shot. He has scored in three straight games.
"I think we rely on our structure a lot throughout the game and we kind of just wait for mistakes," Geekie said. "Teams are good. Sometimes it takes 60 minutes to finally see a breakthrough. Tonight, we saw a couple go in a little earlier than that.
"But we all kind of play the same way. There's not really any difference between the four lines. We're all, kind of, workers."
Fraser Minten scored with a snap shot on a 2-on-1 at 8:39 of the third period for the 6-2 final.
NOTES: Bruins forward James Hagens left early in the third period after taking a crosscheck to the back from Penguins defenseman Samuel Girard.