The victory moved Seattle within a point of Vancouver, which is one point behind West leader Dallas.
Starting in place of the injured Obafemi Martins, Barrett scored in the 4th and 38th minutes to help the Sounders beat their regional Cascadia Cup rivals for the first time in six tries.
A former teammate of Whitecaps coach Carl Robinson when the two were with Toronto, Barrett opened the scoring after taking a pass from Clint Dempsey and converting a one-on-one against goalkeeper David Ousted.
Barrett doubled the lead when Vancouver defender Kendall Waston failed to close him down on the left. The striker beat Ousted with a shot to the far post.
SAN JOSE 2, COLUMBUS 0
Chris Wondolowski scored his 99th MLS goal as San Jose beat 10-man Columbus.
Wondolowski opened the scoring in the 55th minute, heading in Jordan Stewart's cross. It was Wondolowski's sixth of the season and his first at the Earthquakes' new Avaya Stadium.
Shea Salinas added a goal for the Earthquakes in the 60th minute.
The Crew was down a man after Mohammed Saeid picked up his second yellow card in the 33rd minute.
HOUSTON 3, PORTLAND 1
Will Bruin scored twice to lead Houston over Portland.
Bruin opened the scoring with a header in the ninth minute and added an insurance goal on a chip shot in the 83rd to help the Dynamo win back-to-back games for the first time this season.
Fanendo Adi equalized for the Timbers in the 48th minute, shirking a challenge from DeMarcus Beasley and finishing Diego Valeri's pass.
Houston's Giles Barnes made it 2-1 with a blast after a patient back-and-forth with Alexander Lopez in the middle of the box.
NEW ENGLAND 1, TORONTO 1
Toronto's Michael Bradley scored his first goal of the season to give the Canadian club a point from the visit to New England.
Juan Agudelo scored in the 32nd minute for New England.
Bradley used a nice individual effort to equalize in the 53rd minute. He shielded his defender down the field, beat two more Revolution players and sent a shot inside the far post.
MONTREAL 4, REAL SALT LAKE 1
Montreal's Andres Romero scored twice as the Impact won for the first time this season, beating Real Salt Lake.
Laurent Ciman and Dilly Duka also scored for the hosts in rainy conditions.
Devon Sandoval scored for Salt Lake.
With assistant Mauro Biello filling in for suspended head coach Frank Klopas, the Impact scored more than twice for the first time in 25 matches dating back to last season.