The former Liverpool skipper, who starred in the 2-1 win over Mexican giants Club America in the International Champions Cup at the weekend, came on at half-time at the Rio Tinto Stadium in Utah.
Gerrard missed a fine opportunity to hand Galaxy the lead with 15 minutes remaining when he exchanged passes with Robbie Keane, but saw his effort sail high over the crossbar.
RSL won the game as Aaron Maund proved to be the unlikeliest of goalscorers.
The journeyman defender fired home his first professional goal three minutes from time to help his side set up a clash against the winner of next week’s quarter-finals meeting between the Houston Dynamo and Sporting Kansas City.
After the match, Gerrard could not hide his disappointment, telling Galaxy TV: “It’s always tough when you lose on the road, especially when it’s at the end of the game.
“We had some good chances to at least take the game to extra-time. I’m guilty of missing one, so I take responsibility for that, but the big game this week was always going to be Friday.
“We move on, we can’t change the past. We will try to get back to winning ways on Friday.
“It’s been a whirlwind change over the last week or two. I’m still searching for 100 per cent fitness but I can feel it coming.
“I’d be very frustrated and disappointed if I wasn’t getting chances whilst the chances are there and I have full belief in myself that those chances will sooner rather than later go in the back of the net.”
Gerrard is now expected to make his MLS debut against San Jose Earthquakes next Saturday morning.