Despite plenty of chances, this weather-delayed clash in Chester, Pa. ended without a single goal.
The game was delayed half an hour after the interval as lightning strikes flashed across the sky around the Delaware River.
Philadelphia keeper Zac MacMath had arguably his best game of the season, coming up especially well with a reflex save on a short-range Diego Valieri shot.
The Union had some excellent chances late, the choice of which was a Leo Fernandes strike from range which was past Donovan Ricketts but struck the post.
The result preserves Portland's all-time unbeaten run against Philadelphia. In four games, the Timbers are 2-2-0 against the Union, holding the Pennsylvania side to just one goal.