Romain Alessandrini scored twice as the Galaxy ended their four-match winless run with a 3-1 victory at Red Bull Arena.
Giovani dos Santos was on target from the penalty spot, while Galaxy right back Bradley Diallo was shown a second yellow card in the 90th minute.
Daniel Royer pulled a goal back in stoppage time but it could not prevent the Red Bulls' 13-month home unbeaten streak from ending — a regular-season run dating back to April 2016.
The Galaxy are seventh in the Western Conference — two points outside of the playoff places — while the Red Bulls are fifth in the East.
Liam Ridgewell's 50th-minute strike canceled out Julian Gressel's opener for Atlanta at Providence Park.
The Timbers almost claimed maximum points in stoppage time, but David Guzman's effort hit the post.