The Colorado Rapids displaced momentary Western Conference leader FC Dallas, while the Montreal Impact extended their winless run to six games.
Colorado, which momentarily lost its spot atop the Western Conference following FC Dallas' win earlier in the day, moved back to the summit with its eighth win of the season.
Sjoberg scored the game's only goal at the CenturyLink Field in Seattle, heading in from a corner in the 43rd minute after losing his man in the box.
The goal came in controversial circumstances with Rapids forward Kevin Doyle appearing to put the ball out for a goal kick, but a corner was ruled in favor of the visitors, from which they scored.
Seattle mounted pressure on Colorado in the closing stages as the Sounders searched for an equalizer, but they could not avoid back-to-back losses.
Dallas kept up the pace with Colorado courtesy of a 4-2 come-from-behind win at the New England Revolution.
Tesho Akindele put Dallas ahead five minutes into the contest but two goals in the space of three minutes from Juan Agudelo and Lee Nguyen turned the game on its head.
But Atiba Harris netted an equalizer 10 minutes later, and Dallas sealed the result with a goal from Fabian Castillo and then Akindele's second of the evening in the second half.
Dallas remains two points behind the Rapids in the west, while New England is three points off the bottom in the Eastern Conference after the Chicago Fire won their second game of the season.
It was a battle of the bottom teams in each conference, and it was Chicago that came out on top against Houston Dynamo 1-0 courtesy of Arturo Alvarez's third-minute strike.
Meanwhile, the Didier Drogba-less Montreal Impact are now six games without a win after suffering a 2-1 defeat to Orlando City.
Montreal, which set the pace at the start of the season, took an early lead through Ignacio Piatti, but Cyle Larin's goals either side of halftime saw Orlando take the three points in front of its home support.
New York City FC missed the opportunity to move top in the east after suffering an embarrassing 7-0 defeat to local rivals the New York Red Bulls.
Real Salt Lake won 3-1 at Sporting Kansas City, while Toronto FC and Columbus Crew played out a scoreless draw.