RSL were rewarded for their early dominance when Albert Rusnak's shot squirmed into the net through Drew Moor's legs. Damir Kreilach plumped up his team's cushion when he steered a shot into the bottom corner in the 76th minute.
Corey Baird set the tone for the rest of the fixture when he struck the woodwork six minutes into the match. Real Salt Lake looked as if they wanted to finish off the match early, and swarmed upon Colorado in the opening stages. Their pressure paid off Irwin when palmed Douglas Martinez's cross to Rusnak, whose shot eventually squeezed its way into the onion bag.
Colorado didn't improve. Real Salt Lake continued to outdo their opponents in energy and invention, but it took Irwin upending Martinez in the area for what looked like a sure-fire second for RSL.
But Irwin made amends with a strong left hand far down to his right and by blocking the follow-up effort from Nick Besler.
The reprieve was only temporary. Kreilach converted a skimming effort from outside the area when the broadcast was interviewing Rapids head coach Robin Fraser. The exchange was cut short in awkward fashion.
The match trundled toward its close. Colorado attempted a couple of long-range shots near the end but Zac MacMath seemed to appreciate having something to do. Colorado fans will expect improvement when their team faces Sporting Kansas City, who were defeated in dramatic fashion by Minnesota United earlier in the evening, on Friday.