The Stars remain atop the Central Division with 91 points.
"We laid an egg tonight, flat-out," Stars coach Lindy Ruff said. "We were flat. I probably would have risked pulling the goalie, even with 5-6 minutes [left], but we were flat. We would just be handing them another one. When there's no energy, and there's no battle, for me it's just get through it and get out of here."
The Kings scored twice in the opening 5:25 of the first period. Versteeg scored 23 seconds into the game when he redirected Scuderi's slap shot from the left point past Lehtonen.
Toffoli made it 2-0 with a tap-in at the near post at 5:25 of the first off a Dallas turnover. After Kris Russell slipped near the Dallas blue line, Nicholas Shore gained possession. Shore and Toffoli traded passes before Toffoli scored inside the near post.
"Too many mistakes, I think, mental mistakes," Stars captain Jamie Benn said. "We give up a goal on the first shift of the game, a couple bad turnovers hung our goalies out to dry."