Alex Iafallo and Nate Thompson also scored for the Kings (12-20-3), who ended a four-game losing streak. Jonathan Quick made 27 saves.
"Tonight, I don't think there was any doubt in anyone's mind that we should have won that hockey game," Kings defenseman Drew Doughty said. "We played a full 60 minutes, and it is really good Kings hockey right there. We need to do it again. And again."
WATCH: [All Jets vs. Kings highlights]
Mathieu Perreault scored for the fifth straight game for the Jets (22-10-2), who had a five-game road winning streak end. Connor Hellebuyck made 27 saves.
"Just one of those nights," Perreault said. "Bounce didn't go our way. We had our chances, just couldn't put them in, and they scored on their chances. That's kind of the story of this game really."
Iafallo put the Kings ahead 2-1 at 9:08 of the second period. He has six points (two goals, four assists) during a five-game point streak.
Wagner scored on a breakaway at 18:08 to put Los Angeles up 3-1. It was the first multigoal game for the rookie forward playing in his 23rd NHL game.
The goal came after a sequence where Nikolaj Ehlers put a shot toward an open net that went off the post, the kind of chances Jets coach Paul Maurice said his team struggled to create against a sound Kings defense.
"There wasn't a whole lot of easy ice," Maurice said. "We had 18 shots blocked and they worked hard to get in front of those pucks. They played a real strong game and it was tight, not a lot of easy offense to be had for either team."