David Perron scored twice and Brian Elliott made 28 saves in his regular-season return to Ottawa and the St. Louis Blues handed the Senators their seventh straight loss, 3-1 Tuesday night.
Elliott was traded to the Colorado Avalanche prior to last season's trade deadline for Senators' No. 1 goalie Craig Anderson.
Elliott then moved on to the Blues in the offseason.
Anderson, meanwhile, didn't last four minutes Tuesday for the Senators.
Chris Porter also scored for the Blues, who won for just the second time in their past five games.
Daniel Alfredsson scored his 18th goal of the season for Ottawa.