The Timbers (9-12-6) are only 1-8-4 on the road this season with seven goals scored.
The Union's winless streak reached eight, spanning two months. Since a 3-0 victory at New England on July 17, the Union (8-7-12) have gone 0-3-5.
Philadelphia is 5-1-8 at home.
That winless stretch was nearly snapped in the 88th minute when Justin Mapp sent a cross to Kyle Nakazawa, who clanged a shot directly off the crossbar.
Defender Carlos Valdes' header in stoppage time was saved by Portland goalkeeper Troy Perkins.
Philadelphia rookie goalkeeper Zac MacMath, who gave up four goals in a 4-4 draw against the Revolution on Wednesday, responded with a shutout.
The Union won't play until Sept. 17, when they host Columbus, while Portland will host New England on Friday.
(Copyright 2011 Philadelphia Union. Reprinted by permission)