After nine games, Dempsey finally got on the board in his return to Major League Soccer with Seattle, only to see Los Angeles striker Robbie Keane get a late equalizer that put the Sounders in the position of having to play an extra round in the MLS playoffs.
Dempsey scored off a cross from Lamar Neagle in the 30th minute, but Keane's half-volley in the 78th minute gave the Galaxy a 1-1 draw with Seattle on Sunday night in the MLS regular-season finale.
The result left Los Angeles in third in the Western Conference and put Seattle in fourth, meaning the Sounders will host Colorado in the play-in round on Wednesday night. The winner of the play-in game will face Western Conference regular-season champion Portland in the conference semifinals.
Meanwhile, the Galaxy will take on second-place Real Salt Lake in the two-leg conference semifinals.
"We've had a good run since August," Galaxy coach Bruce Arena said. "We've done a good job and we'll hopefully be healthy by the weekend when we play. We'll be in a good position to be competitive and hopefully win the first series."
The disappointing draw for Seattle in front of another massive crowd of 66,218 capped a miserable final month that wasted a chance to win the Western Conference and Supporters' Shield. The Sounders were winless in their final five games, including a four-game losing streak that was snapped with Sunday's draw.
Seattle hasn't won since Sept. 13 when it defeated Salt Lake, but it will open the postseason with Colorado at home and possibly rival Portland at home.
"We're due for a win. That's the most important thing," Seattle midfielder Brad Evans said. "We're due for a win and I'm really happy we have this game at home."
The Galaxy could argue they should have gotten out of Seattle with a victory due to a blown call late in the first half that negated a Los Angeles goal.
Omar Gonzalez came open at the back post on a corner kick from Landon Donovan and his header beat goalkeeper Michael Gspurning. Seattle midfielder Osvaldo Alonso appeared to clear the ball off the line, but television replays confirmed the missed call.
Gonzalez's header clearly bounced beyond the goal line, kicking up rubber pellets, before Alonso's clearance.
Donovan and Keane were immediately irate, getting in the face of referee Mark Geiger. Keane then turned his barking to assistant referee Greg Barkey, who was standing on the end line for the corner kick.
But Keane's late goal gave Los Angeles the draw. It was his 16th of the season and seventh in the last 12 months against Seattle. The Galaxy closed the season with eight points in their final four games to overtake the Sounders and avoid the extra round of the postseason.
"I don't see it from where I am, but I was told it was about a yard over the line. For some reason, I think we should be able to see that one," Arena said. "We're fortunate to get out of it, not using that as a major sticking point in the game."
The bright spot for Seattle was Dempsey getting his first point. Neagle's cross floated into the penalty area and Galaxy goalkeeper Jaime Penedo got the slightest touch trying to deflect the pass. The touch by Penedo took Gonzalez out of the play due to his momentum. Without breaking stride, Dempsey made a slight adjustment to hit the ball with the outside of his right foot and past Penedo as he tried to get back in position.
Dempsey had gone 590 minutes since his first action for Seattle without a goal or assist.
"I think that was important for him, takes a lot of pressure off of him so he's going to be more confident and allows us to make sure we find him," Seattle coach Sigi Schmid said. "I thought we did a good job of finding him."