Rob Niedermayer and Corey Perry also scored for the Ducks, who have earned 17 of a possible 18 points in their last nine games (8-0-1).
Anaheim has suddenly become the top scoring team in the NHL, with 49 goals.
After being the third lowest scoring team in the league last season, the Ducks have found much-needed offensive punch.
"The team is playing well and everyone is contributing in different areas," said Getzlaf, who also has an eight-game point streak.
His 190-foot empty-netter capped a three-point night and gave him 18 points for the season (six goals, 12 assists). Getzlaf moved into a tie with Pittsburgh Penguins forward Evgeni Malkin for the overall NHL scoring lead.
"It's a matter of things clicking right now, and we have to continue playing the way we are," said Getzlaf, who has six goals and 11 assists during his points run. Selanne has posted eight goals and five assists while on his streak.
Ducks defenseman Chris Pronger also tied Montreal's Andrei Markov and Ottawa's Filip Kuba for the scoring lead among NHL defenseman by generating his 13th point. He assisted on Selanne's second-period goal.
There's little doubt the Ducks are on a roll.
"It's all work. When you do it correctly and do the right things, like going to the net and getting the puck in the corner and digging around, it starts clicking. That's the key, doing your small jobs," said Chris Kunitz, who assisted on second-period goals by Perry and Getzlaf that gave the Ducks a 4-2 lead.
Patrik Berglund and Andy McDonald scored for the Blues, and Chris Mason made 21 saves in the first of the team's five-game road trip. St. Louis is 1-5 after a 4-1 start.
"We did some positive things. I liked our energy," Blues coach Andy Murray said. "We need to clean some things up in our defensive zone. We had a couple mistakes that led to goals."
Paul Kariya, the Blues' leading scorer, left in the second period with an undisclosed lower body injury and didn't return.
"We don't really know yet," Murray said. "I don't know what the extent of the injury is, but he couldn't finish the game."
Anaheim's previous five games had been decided by one goal and it looked as if that trend might continue. The Ducks were up by one goal three times, but the Blues got even twice.
"We've been able to come back in a few games, but this league is too tough to do that," McDonald said. "For whatever reason, we've got to clean it up in a hurry."
Niedermayer took a feed behind the Blues defense from Samuel Pahlsson and scored a breakaway goal just 36 seconds after the opening faceoff.
St. Louis tied it 2:34 later. Berglund forced a turnover in the Ducks zone and swept a backhanded shot around Hiller, who made his third start of the season.
Selanne lofted a shot over Mason's right shoulder on a Ducks power play early in the second to make it 2-1. It was Selanne's ninth goal of the season, and his league-leading eighth on the power play.
The Blues' power play, tops on the road in the NHL, quickly responded. McDonald beat Hiller from the slot to tie it at 2 just 57 seconds after Selanne's goal.
About three minutes later, Perry crashed the net and shoveled the puck past Mason to give the Ducks their third lead. Perry then set up Getzlaf for a blast from the slot that made it 4-2 with 4:37 to go in the second.
Getzlaf sent a shot from the left of the Ducks goal the length of the ice into the empty net with 1:05 to play.
The Blues played just two games away from St. Louis in the first three weeks of the season, but nine of their 13 games in November will be on the road. ... Hiller, a second-year NHL goalie from Switzerland, made his first appearance against St. Louis.
Copyright by STATS LLC and The Associated Press
Arena: Honda Center Location: Anaheim, California
Referees: Bill McCreary, Kelly Sutherland Linesmen: Lonnie Cameron, Scott Driscoll
Attendance: 16,144 (94.0% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Rob Niedermayer (3)
Assists: Samuel Pahlsson, Travis Moen
Patrik Berglund (3)
Teemu Selanne (9)
(Power Play) Assists: Scott Niedermayer, Chris Pronger
Andy McDonald (2)
(Power Play) Assists: Lee Stempniak, Paul Kariya
Corey Perry (4)
Assists: Chris Kunitz, Ryan Getzlaf
Ryan Getzlaf (5)
Assists: Corey Perry, Chris Kunitz