Russell Teibert chipped the ball over to Montero for a left-footed shot over goalkeeper Steve Clark's shoulder.
The Whitecaps (3-5-3) have their second straight. The Timbers (3-6-1) had win three in a row.
In the 35th minute, a whole section of Portland followers joined two Whitecaps supporter groups and some Vancouver fans in leaving their seats to show solidarity with female players impacted by allegations of bullying and harassment by a former coach.
Similar protests were held at two previous Whitecaps matches.
More than a dozen women who played for the Whitecaps and were part of Canada's under-20 talent pool around 2008 have come forward to allege Bob Birarda, a former coach for both squads, acted inappropriately with members of the team. None of the allegations have been proven in court.