If there was any doubt that Toronto's big spending in the off season would mean little on the pitch, it was dismissed on Saturday as the Canadian club won their first game of the 2014 season against one of the league's powerhouse outfits.
Defoe scored twice in the first half, while Toronto's other big signing - Michael Bradley - bossed the midfield for the visitors.
Toronto hit the front in the 17th minute when Jonathan Osorio showed quick feet to turn away from an opponent before sliding a pass to Defoe, who converted from just inside the penalty area.
The 31-year-old English striker paid back a portion of his $8million-per-year salary just seven minutes later, firing home from the edge of the box after Seattle's big-money man Clint Dempsey mishit a back pass.
Bradley, who will earn $6m per year with Toronto, put the pressure on Dempsey to force his international teammate into an error.
One of Toronto's other high-profile signings - goalkeeper Julio Cesar - made a big save early in the second half to deny Sounders striker Obafemi Martins.
In the 68th minute, Martins teed up Dempsey to score but Seattle were unable to find an equaliser as Toronto held on for victory.
In the late match, San Jose Earthquakes began their campaign with a come-from-behind 3-3 draw against Real Salt Lake.
After taking an early lead through Chris Wondolowski, San Jose were torn apart by the visitors in a frantic first half.
Real equalised in the 11th minute when Kyle Beckerman lashed the ball home from outside the box and last season's runners-up took the lead just after the half-hour mark through Joao Plata.
It was 3-1 at half-time as Luke Mulholland scored his first-ever MLS goal, finishing from close range after Earthquakes goalkeeper Jon Busch could only parry Ned Grabavoy's initial shot.
After the break, San Jose started to take control but had to wait until the 75th minute to score their second goal with Victor Bernardez glancing his header past Nick Rimando from a corner.
Real almost scored immediately after Bernardez's goal as Alvaro Saborio hit the post but from then on it was all the home side.
Earthquakes striker Steven Lenhart missed a huge chance in the 89th minute but, in the end, it did not cost San Jose with Bernardez smashing a loose ball into the net in the fifth minute of stoppage time after Rimando failed to clear the danger when punching a lofted pass into the box.
Houston Dynamo made it two wins from as many games with a 1-0 triumph over Montreal Impact, while reigning champions Sporting Kansas City drew 1-1 with FC Dallas.
New York Red Bulls were held 1-1 at home by Colorado Rapids and Philadelphia Union won 1-0 over New England Revolution.
