WASHINGTON - Former US senator Rick Santorum rejuvenated his presidential hopes on Tuesday with victories over front-runner Mitt Romney in Republican nominating contests in Missouri, Minnesota and Colorado.Backed by a wealthy "Super PAC" that pays for attack ads against rivals, Romney had excelled in major contests thus far in the race but he did little campaigning in Minnesota and Missouri."Wow. Conservatism is alive and well in Missouri and Minnesota," Santorum told supporters in St. Charles, Missouri after results came in."I don't stand here to claim to be the conservative alternative to Mitt Romney, I stand here to be the conservative alternative to Barack Obama," he added to cheers from the crowd.Santorum has rebuilt a political career left in tatters in 2006 when voters in Pennsylvania threw him out of the Senate by an 18 percentage point margin. But he still faces an uphill battle for the presidential nomination, considering Romney's vast organizational and financial advantages.Gingrich was not on the ballot in Missouri, allowing Santorum the chance to consolidate conservative voters in the state and compete directly with Romney and Paul, known for his libertarian views.Until Tuesday, Santorum had won only one of the first five Republican contests in the state-by-state battle for the Republican nomination to face US President Barack Obama in the Nov. 6 election.But on the first day of multiple nominating contests in the 2012 primary season, Santorum was the winner in Missouri, where he had 55 percent of the vote to Romney's 25 percent, with nearly all the ballots counted. The Missouri vote was a non-binding primary, but has symbolic value as a measure of support in a big Midwestern state.In Minnesota's caucuses, Santorum had 45 percent of the vote, with 82 percent of the returns counted. In another blow to former Massachusetts governor Romney, US congressman Ron Paul was in second place in Minnesota with 27 percent and Romney was a distant third with 17 percent.It was the first time so far in the 2012 Republican race that Romney did not come in first or second in a state contest, and Tuesday's results may force him to recalibrate and focus more on attacking Santorum.The former Pennsylvania senator is a devout Catholic who is in a battle with former US House of Representatives speaker Newt Gingrich to become the conservative alternative to the more moderate Romney.His victories give heart to social conservatives fighting battles of abortion, gay marriage and contraception in recent days.