11 on target, forcing nine saves out of Rapids 'keeper Joe Cannon.
The home side scored twice within five minutes late in the first half to take the lead. Freddy Adu - who played the full match in behind the front two - ran onto a slide-rule pass from Josh Gros on the left and coolly slotted home from the spot for his fourth goal (35). Then Earnie Stewart doubled the lead after he collected a crossfield pass from Alecko Eskandarian and perfectly placed his shot inside the far post.
United then scored a third midway through the second half when Jaime Moreno danced around three defenders into the area before trying to lay back a pass - only for defender Ritchie Kotschau to turn it into his own goal and he chased from behind (64).
The Rapids pulled a goal back when John Spencer scored his first goal since an Opening Day strike against Dallas, finishing a quick break off a turnover with a low drive from just inside the area.
"I hope we get angry," Rapids coach Tim Hankinson said. "That should be the emotion. We've got too many guys whose heads are down and want a hug and forgiveness and someone to be understanding and none of that belongs. ... Our players have got to be angry. I'm not seeing that."
Hankinson made two changes from the team that lost 1-0 to a nine-man Dallas Burn on a stoppage-time penalty the previous Saturday. Gary Sullivan came into central defense with midfielder Jordan Cila the odd man out, while John Spencer returned to the team in attack for the injured Rey Angel Martinez.
Here's Hankinson's team (4-1-3-2): Joe Cannon - Matt Crawford, Nat Borchers, Gary Sullivan (Joey DiGiamarino 55), Ritchie Kotschau - Kyle Beckerman (Seth Trembly 74) - Chris Henderson (Jordan Cila 65), Antonio de la Torre, Mark Chung - Alberto Delgado, John Spencer
"We had a nightmare in the 90th minute in Dallas three days ago," Hankinson said. "(Wednesday) we basically had 90 minutes of nightmare."
For Spencer, it was his first goal in 14 appearances, the longest goalless drought of his MLS experience. "It was a great ball, but losing a game like this is tough. It's nice when you hit the net, but it's hard. ... Obviously, you won't score goals if you don't have chances. It's easy for a striker to say he's going through a bad spell, but we've got to create more chances. I think we had only one shot, maybe two shots on goal, so it's something we need to work on."