Dylan Guenther and Logan Cooley scored, and Karel Vejmelka made 23 saves for the Mammoth (10-7-2), who have lost five of six (1-3-2).
"It's just frustrating the way it happened at the end," Utah coach Andre Tourigny said. "We lose one battle and I don't think we gave up much before that chance."
On the overtime goal, Killorn brought the puck into the Utah zone and centered it to rookie Beckett Sennecke, who drew Vejmelka out of the crease. Sennecke then slid a pass to Zellweger at the right post, and the defenseman tucked it into the open net.
"Great play recognition. Pretty tight quarter, goalie coming out, two guys coming at him, down the barrel," Anaheim coach Joel Quenneville said of Sennecke's play in overtime. "He sees the play. You're thinking he's got to shoot this thing, and then he makes a beautiful pass. Nice play. Incredible."
Cooley gave Utah a 2-1 lead at 9:19 of the third period on a one-timer from the right circle. He made a diagonal pass from the corner of the Anaheim zone to Mikhail Sergachev at the left point, and Sergachev took a few strides toward the middle of the ice before passing the puck back to Cooley for the goal.
"I like 'Cools', the way he played on both sides of the puck," Tourigny said. "I think he stayed with it, he was composed and I think he played a really good game."
LaCombe gave Anaheim a 1-0 lead at 15:52 of the first, scoring on a one-timer from the slot off a feed from Ryan Strome for his first goal of the season.
The Ducks entered Monday second in the NHL in goals per game (3.67) but were held below that average for the fourth straight game.
"We were scoring so much to start the year," Terry said. "Now, hopefully, getting back on the right side of things can slingshot us offensively."