Guenther, who also had an assist, got around Predators forward Fedor Svechkov and beat Nashville goalie Juuse Saros on a forehand-to-backhand move to win it.
Jack McBain scored the tying goal midway through the third period, and Logan Cooley also scored for the Mammoth (1-1-0). Karel Vejmelka made 21 saves.
Filip Forsberg and Erik Haula scored for the Predators (1-0-1). Saros made 20 saves.
McBain tied it 2-2 at 11:37 of the third period on a rebound of a shot from the point from Sean Durzi.
Cooley gave Utah a 1-0 lead at 2:21 of the first period on a one-timer on a 3-on-1 rush. Predators defenseman Roman Josi turned the puck over in the offensive zone, and Guenther made a cross ice-pass on the ensuing rush to Cooley for the goal.
Forsberg tied it 1-1 at 7:23 of the first on a snap shot from the left face-off circle. Brady Martin, who was selected No. 5 by Nashville in the 2025 NHL Draft, had an assist on the goal for his first NHL point.
Haula gave the Predators a 2-1 lead at 13:13 of the second period on a loose puck in the crease that bounced in off his body.
Josi had an apparent goal overturned 26 seconds into the third period after the Mammoth successfully challenged the play for offside.