Santorum won the GOP presidential caucuses in Minnesota and Colorado, as well as the nonbinding Missouri primary.
Conservatism is alive and well in Missouri and Minnesota," the jubilant former Pennsylvania senator told cheering supporters in St. Charles, Mo. Challenging both his GOP rival and the Democratic president, he declared that on issues ranging from health care to "Wall Street bailouts, Mitt Romney has the same positions as Barack Obama."
Romney finished second in two of the three contests, Missouri and Colorado. But Texas congressman Ron Paul took second place in Minnesota.
Bringing up the rear was Newt Gingrich, the former House speaker who largely skipped Tuesday's contests to focus on Ohio, which votes next month.
Santorum's gamble from a few weeks ago paid off.
The cash-strapped candidate chose to skip ahead in the primary calendar to court conservative electorates in the three states while Romney and Gingrich battled each other in the expensive state of Florida.
The Associated Press contributed to this report.