Seattle shocked Kansas City with a goal in stoppage time for the fifth time in the past eight matches. Barrett scored in his Sounders debut after Clint Dempsey's header clanked off the crossbar and goalkeeper Eric Kronberg was caught out of his net.
Kronberg had been solid in his debut for Kansas City, replacing long-time starter Jimmy Nielsen, but was caught out of position in the goal.
Dempsey came on in the 57th minute just a few days after playing 90 minutes for the U.S. national team in an exhibition loss to Ukraine in Cyprus.
Barrett's goal started with a strong crossing pass by Federal Way's Sean Okoli. Kronberg came out of the net and the deflection allowed Dempsey a clear header. His attempt hit the crossbar but he was able to keep the play alive long enough for Barrett to score and ruin what was a strong opener for the defending MLS champions.
It was the first match played with replacement officials after Major League Soccer's referees and other on-field officials were locked out Friday. There appeared to be no egregious issues with referee Alan Kelly, other than the large number of fouls called. Kansas City was called for 25 fouls and Seattle 15.
Both goalkeepers made their debuts as the No. 1 options for their clubs. For Kansas City, Kronberg's first match as the successor to Nielsen was a success for the first 93 minutes. He was peppered by chances throughout by Seattle and denied each one until the end. It was the first time in 90 matches someone other than Nielsen started in goal for Kansas City.
Stefan Frei wasn't challenged as much in Seattle's goal, but came up with the shutout.
Dempsey's minutes were slightly surprising given his recent schedule. After playing against Ukraine, Dempsey traveled all day Thursday and trained with the Sounders on Friday. It was his first training with the Sounders since the end of last season after spending the winter on loan with English Premier League club Fulham.
Twice in the second half, Seattle had scoring chances bounce through the goal mouth but fail to find the back of the net. Lamar Neagle's cross in the 53rd minute deflected off Kronberg, but was behind Obafemi Martins. Fifteen minutes later, Kenny Cooper collected a header in the penalty area and beat Kronberg from a shallow angle, but the shot rolled wide.