Tampa Bay won for just the second time in nine games and moved within four points of Boston for the final playoff spot in the Eastern Conference.
Matt Walker had a goal and an assist for the Lightning, who won their 10th road game in 25 tries this season. Brandon Bochenski had the other Tampa Bay goal and Antero Niittymaki stopped 28 shots.
It was Washington's first game since officially capturing the Southeast Division title. The Capitals did so without playing on Thursday, clinching the division crown when second-place Atlanta lost to Columbus.
Alex Ovechkin had two assists Friday and Semyon Varlamov stopped 24-of-27 shots.
Lecavalier's goal, coming with 4:48 to play in the second period, was at first overruled because the officials felt he hit the puck with a high stick. Replays, however, showed the puck actually bounced off Lecavalier's body and the goal was allowed.