With 2:44 left the Lightning's Dominic Moore attempted a clearing pass that went right onto Chimera's stick and the Washington forward blasted it home for the equalizer -- his second tally of the game.
Matt Hendricks and Alexander Semin scored in the shootout, handing the Caps their second straight win to start the season.
Vokoun ended with 28 saves, weathering two 4-on-3 Tampa Bay power plays in overtime.
Lightning goalie Duane Roloson stopped 38-of-43 shots.
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