Keon Daniel notched his first career goal in the 24th minute for Philadelphia, heading a cross from Michael Farfan past Real Salt Lake goalkeeper Nick Rimando.
Philadelphia (6-3-4) remains unbeaten at home (4-0-3).
Real Salt Lake improved to 2-2-2 on the road and 6-3-3 overall.
The Union have a four-match unbeaten streak and moved into a tie for the Eastern Conference lead with the New York Red Bulls.
Neither Real Salt Lake nor Philadelphia could convert good scoring opportunities in the last 15 minutes.
The best was a header by Union forward Danny Mwanga in the 83rd minute that sailed just over the crossbar.
(Copyright 2011 Philadelphia Union. Reprinted by permission)