The Stars, who suffered through a mid-season slump that appeared to have taken them out of the playoff race, have won five out of six games and earned a point in the one game they lost in that stretch.
Dallas moved into a tie with San Jose for seventh place in the Western Conference playoff race and trails Pacific Division-leading Phoenix by two points.
The Stars broke a scoreless tie with second-period goals from Radek Dvorak and Tomas Vincour.
It remained a 2-0 game until Michael Ryder scored into an empty net with 1:28 remaining in regulation.
Lehtonen lost his shutout bid with 30 seconds to play when he gave up a score to Sam Gagner.
Other than the three goals, Dallas put just 10 shots on net for the entire game against Nikolai Khabibulin.
Dallas opened a three-game road trip that will also take the Stars to Calgary and Vancouver.