Vancouver were quicker off the blocks, as Gershon Koffie attempted a 35-yard shot after just six minutes but failed to keep it on target.
The game went flat thereafter, and came into life only in the 19th minute when Sounders' Johnson had his shot from outside the penalty area saved.
A minute later Jeff Parke came close with a header for Sounders before Brad Evans saw his right-footed shot in the 25th minute saved.
Both sides continued to create chances thereafter, but it was only in the 64th minute that the deadlock was broken when Montero shot home from close range to give the hosts the lead.
Montero came close to adding to his tally just five minutes later, while soon after Johnson could have made it 2-0.
Johnson eventually etched his name on the scoresheet in the 86th minute when released by Evans, finding the target from close range with his left foot to wrap up a 2-0 win for Sounders.