Michel, who replaced Kenny Cooper in the 58th minute, scored in the 87th minute after he tapped a shot into the right corner of the net from the top of the goalie's box. Michel rebounded a missed shot by David Ferreira before scoring his third goal of the season.
Michel set up FC Dallas' first goal in the 65th minute when he arched a free kick to Matt Hedges. Hedges redirected the pass with a header from about 10 yards away that bounced off the ground and into the top left corner of the net.
FC Dallas improved to 11-11-1 with its third victory in its past 20 matches.
Seattle (15-12-6) has lost four straight. The Sounders also are on a six-game winless streak in which they have failed to score more than one goal in a game. Clint Dempsey came close to scoring in the 80th minute, but pulled a free kick just wide left of the net.
The game was the final home game for Dallas coach Schellas Hyndman. Hyndman announced Friday that he is stepping down as coach at the end of this season after taking over in June 2008. Before joining FC Dallas, Hyndman spent 31 seasons as a college head coach, including 24 at nearby SMSU. Hyndman led the club to the 2010 MLS Cup and also became the became the first FC Dallas coach to win MLS Coach of the Year honors.