Johnson's blast from the point got past a screened Michal Neuvirth and came only 1 minute after Alexander Semin had pulled the Capitals into a 1-1 tie with a goal 13:09 into the middle frame.
Cody McLeod also for the first time this season and Jean-Sebastien Giguere made 25 saves for the Avalanche, who began a four-game homestand with a victory.
Neuvirth ended with 26 saves for Washington, which fell to 4-5-0 under newly hired Coach Dale Hunter.
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