The Capitals moved within two points of Florida for the lead in the Southeast Division. Washington had lost three straight since downed Florida Feb. 7. That streak ended with the help of 22 saves from Tomas Vokoun against his former team.
Thomas Fleischmann beat Vokoun with a slap shot in the final minute of the opening period and that was all the scoring until Washington put together its late comeback.
Ovechkin scored on the power play, his 24th goal of the season, 4:47 into the third and Semin delivered the tiebreaking goal with 6:33 to play.
Jose Theodore stopped 39 shots for the Panthers.