The five goals were the most scored by a team in the first half of a game in Major League Soccer history, an unprecedented blitz that came shockingly easy for FCD as Salt Lake's back line crumbled from the opening whistle.
RSL's ugliest performance of the season left coach Mike Petke at a loss for words as he tried to rally his troops at halftime.
"I'm trying to remember watching a game, being part of a game, when it was that ridiculous," he said. "And I can't.
"It's tough coming in at halftime like this, down 5-0. What do you say tactically in that moment? What do you change in that moment? The damage has already been done."
And that damage was monumental. It included three goals by FCD winger Roland Lamah in the first 31 minutes, all set up by Dallas players flashing past flat-footed defenders to get to long balls that left Lamah facing either an open net or a one-on-one situation with RSL goalkeeper Matt Van Oekel, who had no chance to make the stops.
Maxi Urruti and Tesho Akindele also scored before the first-half whistle to put RSL (4-10-2, 14 points) in a 5-0 halftime hole.
It was far too deep to dig out of. Salt Lake got two back as Omar Holness finished a sweet pass from Joao Plata in the 70th minute and Kyle Beckerman headed in a corner kick two minutes later.
Dallas (6-2-5, 23 points) got the last word as 16-year-old rookie Jesus Ferreira son of former FCD league MVP David Ferreira scored his first MLS goal in the 89th.
"I don't know if there are positive to take out of this," said defender Chris Wingert, who was then asked to rate the night on a scale of one to 10. "Maybe I'm at a one. If we hadn't come out and fought if we'd come out and quit in the second half, I'd be at a zero. It's still not near good enough."
The loss comes on the heels of another horrific outing, a 5-1 defeat at Houston on Wednesday that left everybody connected with RSL wondering just what is going on. Petke said fatigue was an issue the club has played six games in three weeks, and 12 players, including keeper Nick Rimando, were missing due to injuries, national team commitments and, in the case of Luis Silva, a wedding. But the coach said there were much bigger issues at play, including a lack of effort.
"I think for some people, yes, absolutely," he said. "We talk a lot about it. It's like a broken record now. … Some if it's an effort problem. Some of it's a talent problem with certain players. And some of it's not accepting the responsibility that they have as players as an organization.
"I have to take the gloves off now because I've been protecting, I've been taking blame. A lot of it has to do with players not accepting their responsibilities."
R RSL played its sixth game in three weeks and was missing 12 players, including goalkeeper Nick Rimando.
• RSL is now 3-25-3 when playing in Texas.