The Capitals, who hadn't scored more than five goals in any of their first four games, tallied five in the opening 15 minutes against the Panthers. The last time Washington scored five goals in a period was on Feb. 12, 2003, in a 5-1 win at Atlanta.
Olie Kolzig had 34 saves, Jamie Heward and Matt Bradley scored unassisted goals and Richard Zednik had two assists for the Capitals.
Florida goaltender Alex Auld was removed at 12:36 after yielding four goals on 12 shots. Josef Stumpel and Nathan Horton scored power-play goals for the Panthers, who were 7-0-1 against the Capitals last season.
Washington's first two shots produced the game's first goal with 1:28 elapsed. After Zednik charged down the right side and took a shot that trickled behind Auld into the crease, Semin tapped in the rebound for his team-high sixth goal.
Stumpel tied it less than five minutes later, scoring his first goal of the season on Florida's initial power-play opportunity.
Washington then scored four goals in just over seven minutes. Chris Clark started the onslaught at 7:08, and Heward made it 3-1 by scoring on a straight-on slap shot from about five feet inside the blue line.
Auld's night ended 39 seconds later, when Kris Beech scored off a pass from Semin. Backup goalie Ed Belfour fared no better at the outset, yielding a goal to Bradley within two minutes of his entering the game.
Although the Capitals rarely have the opportunity to protect a four-goal cushion, they did so masterfully in the second period, killing a 5-on-3 power play and keeping Florida scoreless despite being outshot 13-4.
Horton scored with 11:48 left off a pass from Stumpel.
Notes: The Capitals assigned D John Erskine to Hershey Bears of the AHL. ... Florida has at least one PP goal in five straight games. The Panthers came in ranked second in the NHL in PP percentage (28.6). ... Semin (6-2-8) took over the team scoring lead from Clark (2-5-7). ... Washington's Alex Ovechkin was held without a point for the first time since the opener.