Nate Jaqua scored and Lamar Neagle added a penalty kick in the first half and Terry Boss and the Seattle defense held off a late Galaxy surge to preserve the victory.
Seattle got out to a quick start in the 15th minute, but Neagle’s apparent goal was called back when the linesman raised his flag to signal offside.
Jaqua made up for it soon after, though, knocking in a ball from Neagle to put Seattle up 1-0.
Mike Fucito nearly doubled the lead two minutes later, but his shot was saved at the post by suspended Galaxy goalkeeper Josh Saunders.
LA got their first attempt on goal in the 26th minute when Hector Jimenez got past the Seattle defense, but Boss made a great stop and Adam Cristman missed high on the rebound and Seattle held on to the 1-0 lead.
In the 30th minute, Fucito got into the box on a run and was taken down for a penalty. Neagle hammered the shot low and to the left to beat Saunders for the 2-0 lead and Seattle held that lead to halftime.
To start the second half, Seattle earned a free kick just outside the box and Servando Carrasco blasted a shot that was stopped by the LA defense. David Estrada got his head to the rebound, but his putback attempt missed just over the bar and the lead held at 2-0.
The Galaxy pulled one back in the 73rd minute when Cristman got to a ball in a scramble in the box and knocked it to the net to make it 2-1 in favor of the Sounders.
In the 88th minute, Sounders FC Academy midfielder Aaron Kovar got a strong shot from the top of the box, but pushed it just wide. In the final moments of the match, Cristman got away on a break, but Boss slid in to slow him down and the ball rolled away for a goal kick and the match ended on the restart with the Sounders remaining unbeaten and untied to remain atop the MLS Reserve League.
Sounders FC - Nate Jaqua (Lamar Neagle) 18; Lamar Neagle (PK) 30.
LA Galaxy - Adam Cristman 73.
Sounders FC - Lamar Neagle (caution) 48; Mike Fucito (caution) 64; Miguel Montano (caution) 89.
LA Galaxy - None.
Sounders FC - Terry Boss, Zach Scott, Patrick Ianni, Taylor Graham, Leo Gonzalez, Pat Noonan (David Estrada 46), Servando Carrasco, Michael Seamon, Lamar Neagle (Miguel Montano 60), Nate Jaqua (Aaron Kovar 70), Mike Fucito.
LA Galaxy - Josh Saunders, Bryan Jordan (Howe 78), Dan Keat, Kyle Davies, Ryan Thomas, Dustin McCarty, Jovan Kirovski, Paulo Cardozo (Justin Dhillon 72), Hector Jimenez, Adam Cristman, Miguel Lopez (Jack McBean 60).