Last season's champion, Toronto suffered a 2-0 defeat to the Columbus Crew at BMO Field .
Goals either side of half-time from Federico Higuain and Gyasi Zardes saw Columbus to victory.
Higuain volleyed in the opener in the 44th minute, getting on the end of a Milton Valenzuela cross from the left.
Just 52 seconds into the second half and it was 2-0, Zardes finishing clinically after a beautiful through ball from Pedro Santos.
A fast start helped the Dynamo crush Atlanta United 4-0 in their opener at BBVA Compass Stadium.
Andrew Wenger tapped in the opener in the fifth minute before Philippe Senderos headed in a cross midway through the first half.
Mauro Manotas made it 3-0 in the 27th minute and Houston added another late in the half through Darwin Ceren after a Brad Guzan mistake, giving highly touted Atlanta an opening-day wake-up call.
The New England Revolution were reduced to nine men during their 2-0 loss against the Philadelphia Union and Orlando City worked out a 1-1 draw with D.C. United despite having to come from behind a man down.