Lehtonen has struggled in goal of late, having lost four of his previous five starts. He let a two-goal lead get away 24 hours earlier against Colorado in a 4-3 loss.
He bounced back, however, to record his first shutout of the season and the 22nd of his nine-year career.
Dallas could not provide any offensive help until the third period, but Jaromir Jagr gave the Stars the lead 6:34 into the final stanza with his 12th goal of the season.
Ray Whitney brought Dallas some insurance just over 4 minutes later.
Los Angeles had a three-game winning streak snapped. Jamie Quick gave up the two goals on 21 shots.