Johnson turned aside all 12 shots he faced in the final period, stopping Florida on a 4-on-3 power play late in the game to preserve the lead for Pittsburgh, which reached the 100-point plateau.
Zbynek Michalek scored with less than 8 minutes left in the third period to give the Penguins their first lead.
Jack Skille and Clay Wilson scored and Scott Clemmensen stopped 30-of-33 for the Panthers.
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