Tomas Fleischmann added two goals and two assists for Washington, which won its second straight game. The Capitals hadn’t won consecutive games since beating Atlanta and Philadelphia on Jan. 6 and 9.
Boyd Gordon also scored for Washington and Alexandre Giroux got his second NHL goal. His first came in Friday’s 5-1 win over Toronto.
The Capitals are 2-0-1 since goalie Olie Kolzig returned Thursday after missing 13 games with a knee injury. Kolzig made 30 saves against the Lightning.
Filip Kuba scored a power-play goal for Tampa Bay.
An early Toronto miscue helped the Capitals take the lead Friday, and a Tampa Bay mistake gave Washington another first-period gift Sunday.
Defenceman Dan Boyle lost the puck near the blue line, and Fleischmann then beat goalie Johan Holmqvist near the left circle for a 1-0 lead at 5:31.
Fleischmann made it 2-0 with 6:20 left in the period on a long slap shot. Tampa Bay coach John Tortorella pulled Holmqvist for Marc Denis a few minutes later.
Semin then scored on the first three Washington shots of the second period.
He scored a power-play goal at 1:14, converted a backhander at 6:45 and scored on a long wrist shot 8:18 into the period for a 5-0 lead. The fans then littered the ice with hats, and Tortorella put Holmqvist back in, but the damage was done.
Notes: Fleischmann also scored the final Washington goal in Friday’s win over Toronto. … The Capitals have outscored opponents 6-0 in the first period of their last three games. … Tampa Bay had won five of the first six games with Washington this season. … Six of Kuba’s 11 goals have come on the power play.