The Sounders remain undefeated through six matches this season thanks to a two-goal second half at Lumen Field in Seattle.
Entering the contest, Seattle had 13 points from their first five matches for the second time in the last three seasons – the only team in the last 20 seasons to have at least 13 points after five games more than once.
The Sounders stayed hot courtesy of Xavier Arreaga and Brad Smith – the former opening the scoring in the 57th minute.
Smith doubled the lead with 17 minutes remaining when the Socceroos full-back pounced for his third goal of the season.
The Sounders are four points clear of LA Galaxy in the Western Conference, while Sporting Kansas City are a point further back in third following their 3-0 win over Vancouver Whitecaps.
LAFC is bottom of the west with five points from five matches in 2021.
Former Juventus and Real Madrid forward Higuain was the hero for Inter Miami, which prevailed 3-2 in a thriller at Cincinnati.
Higuain scored the winning goal five minutes from the end after Cincinnati's Nick Hagglund has restored parity three minutes earlier.
David Beckham's Inter Miami – led by former Manchester United team-mate and manager Phil Neville – raced out to a 2-0 half-time lead via Brek Shea and Higuain before Cincinnati rallied with goals from Alvaro Barreal and Hagglund.
Former Argentina international Higuain, though, had the final say with his fourth goal of the season.
Elsewhere, New England Revolution topped defending champion Columbus Crew 1-0 and Orlando City beat DC United by the same scoreline.
Orlando has opened the season unbeaten in its first five games (W2 D3). The Lions have lost just three regular-season matches since the end of the MLS is Back Tournament, fewer than any other team that was in MLS both last season and this.