Anaheim, which had an eight-game winning streak snapped on Friday in Chicago, has won 19 of 21. The Ducks have won nine of their last 11 on the road and lead the NHL with 79 points. They are 20-0-2 at home.
Matt Beleskey and Cam Fowler also scored for the Ducks, who have a league-best 37 points on the road. Andersen (12-2) has won three straight.
Barret Jackman and Jaden Schwartz scored third-period goals for St. Louis, which has lost back-to-back games in regulation for just the second time this season.