In their stead, a pair of guys seeing their first Major League Soccer action punished RSL, handing the Western Conference foe a 2-0 defeat.
"Tonight they got shown that that team isn't weaker than we are," Kreis said. "The guys that played, their 11 was better than our 11."
L.A. midfielder Mike Magee scored his sixth goal of the season when he put his head to a Juninho cross in the sixth minute to ignite the Galaxy scoring.
Just minutes later, L.A. got a goal from forward Charlie Rugg, who was making his Major League Soccer debut in place of an injured Keane. Rugg tapped in a cross from teammate Hector Jimenez, deflating a crowd of 17,655.
Kreis said his team was in "an absolute lull" to start the match. Midfielder Javier Morales called RSL's first 20 minutes "terrible."
"We have to be ready to play against the Galaxy," Morales said, "not against players. So it's not an excuse. Even worse because [five regular starters] didn't play."
RSL was missing key players, too. Forwards Alvaro Saborio and Robbie Findley, who were injured during Friday's training, were both late scratches. Nevertheless, RSL wasn't making excuses for the performance.
"If we didn't have a strong lineup out for our team, I don't know what a strong lineup is," midfielder Ned Grabavoy said. "That's a good enough team to get a result against anybody."
Salt Lake settled into the match as the game progressed, but couldn't crack Galaxy keeper Brian Rowe, who was also making his first MLS appearance.
RSL saw long shots from Kyle Beckerman, Tony Beltran and Joao Plata all saved. The team had a chance to cut its deficit in the 17th minute, when midfielder Luis Gil fired a shot from inside the box, but sailed it over the crossbar.
In one sequence, with RSL on the attack late in the game, forward Olmes Garcia struck the crossbar, Morales banged a shot off the post and defender Nat Borchers had his shot saved by Rowe, who recorded the shutout.
Storylines L.A. shuts out RSL
R The Galaxy play without five regular starters but still win.
• Charlie Rugg, in his first MLS appearance, scores L.A.'s second goal.