"They obviously gained some momentum in the second," LaDue said. "We took a couple penalties we shouldn't have. I thought we came out strong in the third and we executed to our game plan, and it paid off."
Drew Doughty had two assists and has 301 assists and 401 points in his NHL career. Kings GM Rob Blake is the only other defenseman in Los Angeles history to reach both milestones.
Connor McDavid scored his seventh goal in the past three games, and Leon Draisaitl had a power-play goal for the Oilers (23-25-4), who are 5-2-1 in the past eight games. Cam Talbot made 23 saves.
LaDue put the Kings in front 3-2 on the power play with his second NHL goal. Edmonton challenged for goaltender interference but the play stood as called.
Iafallo scored into an empty net with 1:43 to play to make it 4-2, and Kopitar scored his 21st, also into an empty net, with 1:00 remaining for a 5-2 lead.
The Kings are 24-4-2 when tied or leading after the second period, and boosted their League-best scoring margin in the third period to plus-35.
"These are games we want to win," Clifford said. "We want to have an identity that we're a third-period hockey team, so we came out ready to play."
The Kings took a 1-0 lead 1:10 into the first period on Clifford's second goal, and Kempe made it 2-0 58 seconds into the second with his 16th goal.
"We've been through that scenario too many times this season," Oilers coach Todd McLellan said.
Draisaitl cut the lead to 2-1 at 3:28, scoring the first goal Kuemper allowed after stopping 85 consecutive shots.