After lightning in the suburban Philadelphia area delayed the game for an hour at halftime, the Union came out with the best scoring chance of the game in the 71st minute when Conor Casey unleashed a blast toward the net.
But Ricketts was equal to the task, making a leaping save on the attempt.
The Timbers (8-2-10) remained undefeated in four all-time meetings with Philadelphia on their way to posting an eighth tie in 11 road games this season.
Zac MacMath also turned aside two shots for the Union (8-6-7), which ran its home unbeaten streak to five matches.
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