Espindola scored his seventh goal of the year in the 14th minute with a left-footer off a back-heel feed from Kyle Beckerman.
RSL (15-11-4) doubled its advantage in the 36th when Morales bent a free kick over the wall and into the net, collecting his first goal since June 23.
With the victory, Salt Lake assured itself its fifth straight trip to the MLS post-season.
Bright Dike headed a shot into the net in the 61st minute for Portland (7-15-8).
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