The Stars have turned their season around by winning five in a row and nine of their last 10. The lone loss in that run was in overtime.
A month ago Dallas appeared likely to miss the playoffs for the second straight year but the Stars have used the streak to move in front in the Pacific Division. The Stars began the night three points ahead of second-place Phoenix.
Lehtonen outdueled Jonas Hiller, who suffered a hard-luck loss while being beaten only once in 22 shots.
Dallas has not suffered a loss in regulation since a Feb. 19 setback against Nashville.