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.
Anderson was replaced by Alex Auld after allowing two goals on four shots. Auld turned aside 13 of 14 shots.
The Blues entered the third period with a 3-1 lead after Perron scored his second of the game at 6:35 of the second when he chopped a backhand over the shoulder of Auld.
The goal restored a two-goal lead for the Blues after Alfredsson scored on the power play just 56 seconds into the period.
Sergei Gonchar took a shot that hit Alfredsson's skate at the side of the St. Louis goal, bounced off Elliott and went in.
The first period was much like the second as the Senators failed to gain any big rewards for their efforts.
Despite outshooting and out chancing the Blues in the opening period, Ottawa trailed 2-0 heading into the first break.
Porter opened the scoring with a redirect just 1:37 into the game.
Perron scored his first of the game at 3:49 after picking up a rebound that Anderson couldn't control and scoring before the Senators' goalie could get back into position.
Elliott kept Ottawa off the board with nine saves in the period, including one off Colin Greening who took a pass in tight from Jason Spezza on a 2-on-0 break.
The Senators won't get much relief during their slide as they host the Nashville Predators on Thursday. The game will also mark the return of Mike Fisher to Ottawa for the first time since he was traded to Nashville.
Notes: Senators defenseman Chris Phillips played his 999th game, all with Ottawa. ... Milan Michalek is halfway there as he played his 500th game Tuesday, and 183rd with Ottawa. ... The Blues are 10-0-2 against the Eastern Conference this season. ... The win was the first for St. Louis in Ottawa since Jan. 26, 2000.