Washington halted a three-game losing streak and won for the second time in as many appearances in Pittsburgh this season.
It was a 2-2 game going into the third, but Ovechkin gave Washington the lead with a power-play goal 1:48 into the period.
Ryan Whitney, activated on Dec. 23 after recovering from foot surgery, tied it with his first goal of the season. It was all Washington after that, Tomas Fleischmann scoring the game-winning goal at 8:11 on the power play.
Ovechkin tallied his 29th of the season 3 minutes later and Jeff Schultz finished things off with a shorthanded goal with 1:06 to play. It was Schultz's first goal of the season in 27 games.
Jose Theodore made 26 saves to get the victory. Marc-Andre Fleury allowed five goals on 41 shots.