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.
Anaheim scored three times on its first 11 shots against Brian Elliott, who had a franchise-record, 13-game home winning streak snapped.
Getzlaf scored off a pass from Corey Perry 5:27 into the game. Getzlaf, who added an assist, has 14 points in his last nine games.
Beleskey squeezed a shot through Elliott early in the second period. Elliott made the initial save, but the puck trickled through his legs into the net.
Fowler tallied on the power play with a shot from the top of the circle to push the lead 3-0 midway through the second period.
Schwartz got the Blues to within 3-2 with a power-play goal at 14:31 of the third.
St. Louis is 1-7 against California teams this season.
NOTES: St. Louis LW Alexander Steen returned to the lineup after missing 11 games because of a concussion. ... The Blues have an NHL-best, plus-55 goal differential. ... Anaheim RW Teemu Selanne didn't play in the second of back-to-back games, as usual. The Ducks lost 4-2 in Chicago on Friday. ... RW Chris Stewart played in his 200th game with the Blues. ... The Ducks are 22-3-4 in games in which they score first.