After threatening on several occasions, LAFC finally broke through with a goal as Arango received a deflected pass in the box and his header snuck inside the post and past a diving Stefan Frei.
The draw ensured that LAFC (9-3-3, 30 points) would remain atop the league standings through the weekend. LAFC is 4-2-1 in road games this season.
Seattle striker Albert Rusnak scored in the 58th minute, collecting his first goal since signing with the Sounders (6-6-2, 20 points) in January.
The score capped off a busy three weeks for Rusnak, who was returning to MLS after playing four games with Slovakia's national team.
This gift of a goal was all the Sounders could muster, despite a number of decent opportunities. Seattle was lacking in the final third, with extra passes, hesitant shots, and off-target kicks all scuttling other chances to score.
Raul Ruidiaz, the Sounders' leading scorer, was unavailable due to a hamstring injury.
The Sounders are 4-1-1 in their last six games.
At the other end, Los Angeles' best chances came on fast-developing plays. Frei twice had to make a pair of rapid-fire saves -- first on Arango and Danny Musovski late in the first half, and then on Ryan Hollingshead and Arango in the 64th minute.
Arango led LAFC with four shots, and his pressure eventually paid off with his fourth goal of the season.
Rusnak and Cristian Roldan each led the Sounders with three shots apiece.
Seattle had a 13-11 edge in total shots, but Los Angeles held the 7-5 advantage in shots on goal.
Sounders defender Xavier Arreaga was substituted out of the game in the 74th minute after suffering an apparent hamstring injury.