Michal Handzus and Jarret Stoll also scored in the third period for the Kings, whose 6-0-2 run is their longest since a nine-game streak from Jan. 21-Feb. 6, 2010.
Los Angeles is 3-0-2 at the midpoint of a franchise-record, 10-game road trip.
Jonathan Bernier had 22 saves for the Kings after allowing a goal to Alex Ovechkin on the first shot of the game. Bernier, the backup to Jonathan Quick, has not yielded more than two goals in four starts.
Washington was coming off a 2-0 home loss to San Jose on Tuesday. The Capitals have scored two goals or fewer in nine of 13 games.
Semyon Varlamov made 24 saves for the Capitals, who play their next five games on the road.
It was the only meeting of the season between the teams. The Kings have won four straight over Washington since 2007.
Loktionov put Los Angeles up 2-1 by scoring off the rebound of a shot by Kyle Clifford. Handzus gave the Kings a two-goal cushion with 7:32 remaining, and Stoll applied the clincher less than 1½ minutes later.
The game started incredibly well for the Capitals, who have been blanked eight times this season.
Ovechkin fired a wrist shot from the top of the left circle that soared past Bernier at 18:54. It was the 21st goal for Ovechkin, who had been held without a point in eight of 12 games.
Los Angeles tied it at 10:41 of the second period when Anze Kopitar put in the rebound of a shot by Wayne Simmonds. Kopitar had gone 10 games without a goal.
The third period was dominated by the Kings. It was only the second time in 15 games since Jan. 6 that Los Angeles was involved in a game decided by more than two goals.
Notes: The crowd of 18,398 was the Capitals' 91st consecutive sellout at home. ... Kopitar played in his 310th consecutive game, 14 short of the team record held by Marcel Dionne. ... Washington D Mike Green, who was hit in the head with a puck on Sunday against Pittsburgh, returned after a one-game absence.