Remi Walter scored his first career MLS goal to give SKC the lead before Nicolas Benezet equalized in the 58th minute. Johnny Russell, in a rich vein of form, sealed all three points for the visitors in the 78th minute.
Story of the match
Sporting Kansas City were ahead inside four minutes as Khiry Shelton and Russell combined on the right edge of the box before the latter swung a low delivery across the face of the six-yard area.
Seattle goalkeeper Stefan Frei punched clear only as far as Gadi Kinda, whose rebound effort near the penalty spot was blocked through traffic.
Luis Martins converged on the ball and crucially won possession by poking the ball to Walter, who lashed a spectacular left-footed strike into the top left corner past Frei.
The visitors should have doubled their advantage after three minutes later. Russell flicked a pass into the path of Kinda. The Israeli international swiftly beat a defender at the top of the box and uncorked a right-footed blast that was only narrowly high.
In the 15th minute, SKC goalkeeper Tim Meila corralled Benezet's well-struck shot. He also saved from Cristian Roldan as the first half drew to a close.
On the half-hour mark, Russell asked further questions of the Seattle backline by chipping in a cross from the right end line. Roger Espinoza was there, but his effort was deflected behind for a corner kick.
On Russell's ensuing delivery, the ball skipped through a swarm of bodies and was nearly poked home by Sounders defender Shane O'Neill, whose blushes were saved as his redirect carried inches over the bar.
In the second half, Seattle turned up the pressure. After Meila was lucky to escape with just a yellow card after taking down Cristian Roldan while center back Andreu Fontas blocked a side volley attempt from Jimmy Medranda.
The hosts equalized in the 58th minute as Cristian Roldan glanced Joao Paulo's service to the back post where Benezet was there to nod home into an empty net for his third goal of the campaign.
Cristian Roldan almost went from provider to goal scorer in the 64th minute, his header on target, but Melia produced a phenomenal reflex save at point-blank range.
He then made another fantastic stop on Roldan 10 minutes later, dropping low to his right to smother the shot from the Sounders midfielder.
Sporting Kansas City scored the match-winner on a spectacular sequence as in a dazzling 38-pass sequence, Espinoza charged into the attacking third and played an inch-perfect diagonal through ball to Russell.
The Scottish winger took a touch on the right side of the box and sent a lovely side-footed effort past Frei for his 12th goal of 2021, all of which have come since the start of July.
Seattle went close to a last-gasp equalizer in the 93rd minute, but Cristian Roldan's booming strike rattled the crossbar.
Man of the match: Tim Meila
He made four saves, all of them spectacular as Seattle outplayed Sporting Kansas City in the second half. The 35-year old was at his very best in one of the most important games of the season.