Gibson made a save on Ryan O'Reilly's breakaway after he exited the penalty box at 9:26 of the third period to keep it a one-goal game, but St. Louis went on the power play soon after and Sanford extended the lead to 3-1 at 13:08.
"These low plays around the net were open (on the power play)," Blues coach Craig Berube said. "They did a good job and took advantage of it."
Anaheim entered the game seventh in the NHL on the penalty kill at 85 percent, but St. Louis went 3-for-3 on the power play, the first time it scored three times on the man-advantage in a game since Oct. 24, 2019, when it was 3-for-4 in a 5-2 win against the Los Angeles Kings.
"We're attacking more now, more downhill, trying to attack the net more often, and we're winning puck battles," Sundqvist said. "The last couple games, we've been outworking the penalty kill."
Rakell scored with 9 seconds left and Gibson pulled for the extra skater to make it 3-2. Trevor Zegras, who was selected with the No. 9 pick in the 2019 NHL Draft, had the primary assist for his first NHL point in his fifth game.
"I felt like 5-on-5 we were doing a pretty good job out there," Ducks defenseman Jani Hakanpää said. "We had our looks there to put the puck in, just didn't bounce for us tonight, so just got to keep working, keep grinding here."
NOTES: Sanford has six points (four goals, two assists) in his past three games. … St. Louis has won all four games in Anaheim this season and eight straight at Honda Center, the second-longest road winning streak against a team in its history. The Blues won nine straight at the Arizona Coyotes from Dec. 23, 2011 to March 29, 2017. ... Ducks defenseman Hampus Lindholm missed his second straight game because of an undisclosed injury.