Anze Kopitar and Jarret Stoll each had a goal while Jonathan Quick made 25 saves for the Kings, who have won six of their last seven to get back into the chase for a playoff spot in the Western Conference.
Dainius Zubrus scored the lone goal while Scott Clemmensen made 29 stops for the Devils, who had won nine of 10 coming into the game and hold a six-point lead over the Flyers and Rangers for first place in the Atlantic Division.
The Kings drew first blood at the 10:23 mark of the second period on the power play, as a one-timer by Stoll in the high slot went through a screen set up by Dustin Brown in front of the net.
Los Angeles made it 2-0 a bit over two minutes later as Kopitar's quick shot from the left circle beat Clemmensen low to the far post.
The Kings were awarded a penalty shot with 5:23 to play when a Devil closed his hand on the puck in the crease, and O'Sullivan made it count as from down low he snapped the puck into the left corner of the net for a 3-0 advantage.
Quick needed to make just six saves in the second frame to keep the Devils off the board.
New Jersey made it a 3-1 game with 9:19 to play in the third, as Zubrus' one- timer knuckleball in the slot made it past Quick to cut the score to 3-1.
However, New Jersey was unable to score again despite pulling the goaltender and skating the last 1:05 of the game with a power play.
The Devils almost took a 1-0 lead while on the power play at the 4:07 mark of the first, but the puck was ruled to have been kicked in and after a replay the goal was waived off.
After 20 minutes of play, the game was scoreless as Quick made 13 saves while Clemmensen stopped 12 shots.