Regin (power play) and Milan Michalek (power play) also scored one goal apiece, while Brian Elliott stopped 27-of-29 shots for the surging Senators, who extended their winning streak to a season-high five straight games.
Regin had two assists.
St. Louis got goals from Eric Brewer and Brad Boyes.
Goalie Chris Mason was beaten three times on 30 shots for the Blues, who have lost two of three.
On the power play, Ottawa was 3-for-4 and St. Louis failed to score on its three chances with the man-advantage.
Celebrity Couples of 2014 [PHOTOS]