Boyd's first Major League Soccer goal came off Kalif Alhassan's cross in the 66th minute against Union goalkeeper Zac McMath.
Boyd, the Scottish Premier League's all-time leading scorer, was acquired by the Timbers in the offseason. His goal came with the match tied at 1 after a Portland own goal and Andrew Jean Baptiste's equalizer earlier in the half.
Alhassan added a goal of his own in the 76th minute in the MLS opener for both teams.
The Portland Timbers went 11-14-9 last year and finished out of the playoffs in their inaugural season, but they were 9-5-3 at home where they have the support of their wildly enthusiastic supporters' group, the Timbers Army.
Philadelphia finished 11-8-15 and reached the Eastern Conference semifinals, but the team was active in the offseason, bringing in 14 players and losing 13. Among the players gone are leading scorer Sebastien Le Toux and goalkeeper Faryd Mondragon.
Like last season, the Timbers Army opened the season at home by singing the national anthem before the entire stadium lofted colored cards - small tarps actually, because of a driving rain - in a "tifo" fan display in honor of the team.
Temperatures in the low 40s accompanied the rain when the nationally televised game started. The wind impacted the trajectory of the ball at times when it was airborne.
McMath had a strong first half, fending off five Timbers' shots.
The Union got a scare in the 24th minute when defender Carlos Valdes went down after a collision with Boyd. A stretcher was brought on to the field, but Valdes walked off and was able to return.
Philadelphia midfielder Gabriel Gomez's hard kick from out in front of the box was helped by Jean-Baptiste before it sailed past goalkeeper Troy Perkins for an own goal in the 51st minute. .
But the Timbers evened it in the 54th minute when Jean-Baptiste's header was bobbled by McMath and bounced into the goal.
Jean-Baptiste was selected with the eighth overall pick in the MLS SuperDraft this year out of Connecticut. He got the start Monday night because defender Futty Danso fractured a bone in his left foot during training and will be out four to six weeks.
Boyd was greeted with rousing applause during player introductions at the start of the match. The 28-year-old had 164 goals in 296 appearances in the SPL with Kilmarnock and Rangers. He was that league's top scorer for four seasons.
Another Timbers offseason acquisition, Franck Songo'o of Cameroon, who played last season for Spanish side Albacete. The 24-year-old injured his right knee in training and did not play.
MLS Commissioner Don Garber was at the game.
(Copyright 2011 Philadelphia Union. Reprinted by permission)