Lundestrom scored on a wraparound 34 seconds into the third period to make it 4-2 and on a deflection at 15:16 to get Anaheim within 4-3.
"I just want to keep going and playing my own game here," Lundestrom said. "Of course, good confidence from this game for myself and I just want to keep building on that."
Sanford made it 5-3 on a shorthanded empty-net goal with 1:20 remaining.
The Ducks pulled within 5-4 with 1:00 left on a goal by Ryan Getzlaf.
Anaheim scored first for the fourth straight game when Lundestrom's wrist shot from just below the left face-off dot banked off the far post for a 1-0 lead at 5:04 of the first period.
Jordan Kyrou tied it 1-1 with 57 seconds left in the first when he scored off a give-and-go with Ryan O'Reilly.
Kyrou was called for a double minor for high sticking later in the period, but Husso made eight saves on the power play.
David Perron gave St. Louis a 2-1 lead when he scored off a 2-on-1 at 6:35 of the second period.
"We're staying with pucks," Perron said. "We did have meetings to talk about that on both sides of the puck, critical areas of the ice that we can get to more and score. Critical areas that we have to cover, so we give less Grade A scoring chances against."
NOTES: Sanford has five points (three goals, two assists) in the past two games. … Joshua is the 17th Blues player to score in his NHL debut, and the first since Wade Megan on Dec. 22, 2016. … Lundstrom, at 21 years, 115 days, is the second-youngest player in Ducks history to score a hat trick. Sam Steel was 21 years, 51 days when he scored three goals March 26, 2019. … Ducks defenseman Hampus Lindholm missed a fourth game in the past five with an unspecified injury. ... Ducks defenseman Cam Fowler had an assist to extend his point streak to four games (one goal, five assists).