Afinogenov's first goal of the new season -- with assists by Thomas Vanek and Toni Lydman at 15:02 of the second period -- broke a 1-1 tie and gave Buffalo a lead it would not relinquish the rest of the way.
Goaltender Ryan Miller made 23 saves on 26 shots, as the Sabres won their second straight contest.
Back-up goalie Brent Johnson was beaten seven times on 53 shots, as the Capitals suffered their second straight loss after beginning the new season with three straight wins.
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