It was the 13th straight home win for the Penguins, establishing a franchise record. Pittsburgh has lost only three times in its 22 home appearances this season.
Alex Ovechkin put Washington in front 8:35 into the third period with his league-leading 35th goal.
Jokinen tied it with 8:25 to go in regulation and Matta delivered the game-winner with 1:54 left. Matt Niskanen assisted on both goals.
Michal Neuvirth stopped 33-of-37 shots for the Capitals, who have lost three straight and seven out of nine.