Defenceman Filip Kuba added a goal and two assists, and Nikita Alexeev also scored for Tampa Bay, which snapped a four-game losing streak. The Lightning outshot the Capitals 29-9 through two periods while taking a 5-2 lead, bringing loud boos from an announced crowd of 10,417.
Washington's Kris Beech and Bryan Muir scored in the third period to make it a one-goal game with about 7 1/2 minutes left, but Lightning goalie Marc Denis managed to hold on for only his second win in his last 12 starts.
Alex Ovechkin scored his 23rd goal and had an assist for the Capitals, who had won seven of nine. Jamie Heward scored Washington's other goal.
In the teams' previous meeting, Nov. 28 at Tampa, Washington won 5-2 behind Olaf Kolzig's career-high 48 saves to end its six-game winless drought. That loss began a 1-7-1 slide for Tampa Bay entering Tuesday; for the Capitals, that game was the start of a 7-1-1 roll.
The Capitals have been dominant at the start lately, outscoring opponents 14-4 in the first period of those nine games. But Washington came out flat Tuesday, outshot 17-5 and outscored 3-1 in the opening period.
It took the Capitals 10 minutes just to put their first shot on goal. By that point, the Lightning had taken six shots - and one had gone in, at the 7:34 mark on Kuba's power-play goal off a rebound Kolzig couldn't control.
The Lightning went up 2-0 at the 12:54 mark on a breakaway just as a Capitals power play ended. As they crossed the blue-line together, Lecavalier passed to St. Louis, who scored for the fourth game in a row.
A minute later, Ovechkin answered with his fifth goal in three games. He wheeled around the net, as though looking for someone to pass to, then stopped near the circle, paused and threaded the puck past Denis.
Lecavalier put Tampa Bay up 3-1 at the 17:15 mark on a power-play goal, with Kuba and Dan Boyle getting the assists. Lecavalier, the No. 1 overall draft pick in 1998, put the puck under Kolzig's arm for his 19th goal of the season.
It was 4-1 only 1:35 into the second period on another power play, when Lecavalier passed to a streaking St. Louis, who cut across the net and lifted a backhander past Kolzig. Washington made it 4-2 on Heward's goal six seconds into a power play at the 8:36 mark of the second period, but Alexeev restored the three-goal advantage with 41.7 seconds left in the period.
Notes: Tampa Bay finished with a 35-24 edge in shots. ... St. Louis extended his point streak to six games; he has six goals and seven assists during that span. ... The Capitals recalled LW Alexandre Giroux from Hershey of the AHL. ... Washington's Donald Brashear was scratched because of an injury; the team listed him as day-to-day. The Capitals wouldn't say what type of injury he has.