The former Pennsylvania senator had earlier notched victories in Missouri's primary and the Minnesota caucuses, reigniting his White House campaign and staking his claim as the main conservative rival to frontrunner Mitt Romney.
Call exclusively announced the results of the Colorado caucuses on CNN, telling the network: "It has been very exciting tonight... Rick Santorum surprised a lot of folks."
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According to the unofficial results provided by the Colorado Republican Party to CNN, Santorum won more than 40 percent of the vote, besting Romney's nearly 35 percent.
Former House speaker Newt Gingrich took 12.8 percent of the vote, and veteran Texas congressman Ron Paul finished last with 11.7 percent.
With nearly all of the precincts reporting in Missouri, Santorum was the big winner with 55 percent of the vote, more than double Romney's 25 percent. Paul earned 12 percent, and four percent of voters were uncommitted.
In Minnesota, Santorum won 45 percent of the vote, easily defeating Paul at 27 percent. Romney was a distant third at 17 percent and Gingrich took 11 percent, with 86 percent of precincts reporting.
The results in Minnesota and Colorado are non-binding but will help guide the results at state conventions to be held later.
The Missouri primary is seen as a "beauty contest" as the state will only award its delegates after a March 17 caucus.
