The win gives TFC a bit of revenge for a shootout loss to the Sounders in last season's MLS Cup final.
Altidore's goal came 23 minutes in after he was taken down in the box by Seattle defender Roman Torres, and the USA striker stepped up and netted to give his side a win despite playing without Italian star Sebastian Giovinco, and three other starters.
The win moves Toronto to the top of the MLS table on 19 points.
At the other end of the spectrum, the Philadelphia Union made sure no team in Major League Soccer would go winless this season.
A second-half hat trick from C.J. Sapong earned the Union a 3-0 win over the New York Red Bulls, to give the side its first win in nine matches this season, and first victory in almost nine months.
A stellar goal from teenager Ballou Jean-Yves Tabla saw the Montreal Impact take a 1-0 win over D.C. United. The win is the Impact's second of the season, leaving the side on 10 points, second bottom of the Eastern Conference.
Houston played without injured striker Erick 'Cubo' Torres, but still piled on to Orlando City's tough week, running up four goals in a 4-0 route and handing the Lions their second loss of the week and third of the season.
FC Dallas remained the only unbeaten side in the league, taking a 3-0 win over Real Salt Lake, the LA Galaxy stormed back from two goals down to take a 2-2 draw with the Chicago Fire and The Portland Timbers took a surprising 3-0 loss to the San Jose Earthquakes.