The Cobalt and Claret kept their hopes of a domestic treble alive with an important result that could hurt the 'Caps.
The visitors, with one eye on Tuesday's U.S. Open Cup final, reted a number of starters. Kyle Beckerman, Nick Rimando and Javier Morales were uninvolvedand the questionable Alvaro Saborio was similarly not risked.
Real Salt Lake found the game's lone goal early. Lovel Palmer was unchallenged charging forward from right back, and had the time to serve up an excellent cross to Devon Sandoval, who slipped away from Jay DeMerit to connect a powerful header and put the ball in the back of the net.
The Royals showed little sign of missing their rested key players, out-passing and out-possessing the home side. Deputy goalkeeper Jeff Attinella came up with several key stops, including a 14th-minute smothering of a Vancouver counterattack and a reflexive 36th-minute save to deny Russell Teibert.
RSL (15-10-6) now has the best record in the league, although level-on-points New York has a game in hand and Seattle, trailing by just a single point, has three matches to make up. Vancouver's postseason hopes take a big hit, as the Whitecaps (11-11-8) now trail Colorado and Los Angeles by four points.