The Galaxy grabbed a slim lead in their Western Conference semi-final tie
The Mexican striker on Sunday made good use of a strong individual effort from Jelle Van Damme with a header that deflected off Rapids defender Axel Sjoberg and looped over Colorado keeper Tim Howard.
The Galaxy grabbed a slim lead in their Western Conference semi-final tie, which will conclude November 6 with a return leg in Colorado.
Los Angeles scored despite Colorado's disciplined defense.
"It was very difficult," dos Santos said. "They press every single ball, and they're very compact. Not for nothing are they the best defensive team in MLS."
And Rapids coach Pablo Mastroeni was confident his team could overcome a one-goal deficit when they host the Galaxy at altitude in suburban Denver.
"We're in a really good spot," Mastroeni said. "I like our chances of getting a goal and going into the waning minutes or overtime at altitude, where teams struggle."
The Eastern Conference semi-finals got underway with two Canadian teams getting the jump on two from New York.
In Montreal, the Impact seizing a 1-0 victory over the New York Red Bulls thanks to Matteo Mancosu's stunning half-volley.
The Italian import out-raced two Red Bulls defenders and one-timed a blistering shot just inside the box to the left of keeper Luis Robles in the 61st minute.
Marco Donadel fed Mancosu with a well-timed long ball over the top of the Red Bulls midfield.
Mancosu has six goals in 16 appearances since arriving in July on loan from Serie A outfit Bologna, and has filled the void left by Ivorian star Didier Drogba who hasn't played in a month as he battles a sore back.
"Scoring the goal was an incredible feeling," Mancosu said. "We needed to find the breakthrough and there were a couple opportunities in the first half, but we didn't take them. We started the second half well and then came this beautiful pass from Marco and I was able to hit it well toward goal. When you hit it well, there's nothing the goalie can do."
The Impact successfully stifled the Red Bulls' potent attack.
The visitors' best chance came in second-half stoppage time when Evan Bush parried a close-range shot by Omer Damari into the path of Bradley Wright-Phillips, who fired wide.
Damari was shown a red card seconds later for a late challenge on Calum Mallace, and won't be available for the return leg.
In Toronto, goals from Jozy Altidore in the 84th and Tosaint Ricketts in injury time lifted the hosts to a 2-0 victory over New York City FC.
City, who were without Italian star Andrea Pirlo who is nursing a calf injury, created little offense and had to rely on newcomer Eirik Johansen in goal to thwart several strong Toronto opportunities in the first hour.
The night's action closed in Seattle with the Sounders hosting FC Dallas -- winners of the Supporters' Shield awarded to the team that topped the regular-season table.