For the second week running, the Seattle Sounders relied on their highest-paid player to perform heroics.
Seattle went behind early as Dallas capitalized on a mistake by goalkeeper Stefan Frei. The Swiss shot-stopper jumped for a high-bouncing ball, but caught in the wind, it was just above his fingertips. David Texeira rounded the keeper and headed it into the open net.
Dempsey equalized in the 21st minute, driving home a powerful free kick from distance that hit the crossbar and dropped behind Chris Seitz.
Dallas reclaimed the lead shortly before halftime. DeAndre Yedlin foolishly shoved Texeira in the box to concede a penalty, which Michel converted to make it 2-1.
That lead held out until the 76th minute, when it became Dallas' turn to give away a goal on a mistake. Dempsey's hard, low pass into the six-yeard area was intercepted by Stephen Keel, but the FCD defender turned the ball into his own net to make it 2-2.
Dempsey came up big with late heroics for the second time in as many weeks and scored the winner in the 85th minute, playing a quick one-two with Chad Barrett in the box and bundling in his finish from close range.
Seattle is now 3-2-1 for the season, three points back of MLS Western Conference leader Dallas, which falls to 4-1-1. Dallas remains the league's most potent attack, with 15 goals so far this season.
Dempsey is now the leading scorer in MLS, with six goals so far this year.