Erik Karlsson also scored for the Senators, who snapped a three-game skid.
Tyler Myers scored Buffalo's goal as the Sabres dropped to 1-8 in their past nine home games.
Ottawa's first sustained pressure came five minutes into the game, and Sabres defenceman Josh Gorges batted an airborne puck out of danger as it reached the goal line.
The Sabres received Bronx cheers midway through the period when Zemgus Girgensons' shot was caught by Lehner for Buffalo's second shot of the game and first since the opening moments.
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