WATCH: [All Penguins vs. Kings highlights]
Pittsburgh, coming off a 5-3 loss to the Anaheim Ducks on Wednesday, has won five in a row in the second game of a back-to-back.
Adrian Kempe scored, and Jonathan Quick made 28 saves for the Kings (24-16-5), who have lost a season-high five games in a row.
DeSmith, whose first two NHL games came in relief in losses at the Winnipeg Jets on Oct. 29 and against the Toronto Maple Leafs on Dec. 9, made a right-pad save on Dustin Brown from close range on the first shot he faced, with the Kings on the power play 1:57 into the game.
"They had a great look, and he looked pretty poised in there with the save he made and had to get over there quick," Crosby said.
Hornqvist beat Quick through the five-hole from above the right face-off circle 43 seconds into the game to give Pittsburgh a 1-0 lead.
Several key saves by DeSmith allowed the Penguins to carry that lead into the second period despite being outshot 11-3 in the first.
"They were coming pretty hard," Crosby said. "I thought we just stayed patient, found a way not to let it turn against us where we're down after one. We found a way to kind of hold the lead. Kind of weird the way it works sometimes, but I thought we had a really good third given it's back-to-back nights."