The Kings built a three-goal lead and then turned things over to goaltender Jonathan Quick, who will be on the United States' Olympic roster next month in Sochi.
Boston, after winning two in a row, has dropped the first two outings in a three-game California trip that ends Saturday in San Jose.
Jeff Carter scored for the Kings in the opening period and Williams produced a power-play goal just 44 seconds into the middle period. Martinez soon boosted the lead to 3-0 and Quick took over from there.
Quick gave up a goal to Matt Fraser midway through the second, but Dustin Brown restored a three-score lead with 7:38 to play in the third. That gave Los Angeles plenty of room to survive a goal on a deflection by Justin Florek with 2:13 remaining.