Presidential candidate Rick Santorum won decisively in Minnesota's GOP caucuses on Tuesday, clobbering rival Mitt Romney in a state Romney had won easily just four years ago.

With most of the Minnesota vote in, Santorum won 45 percent of the GOP straw poll, followed by Ron Paul at 27 percent. Romney placed a distant third, while Newt Gingrich placed last.

"Conservatism is alive and well today in Missouri and Minnesota," a triumphant Santorum said in a victory speech from Missouri. The former Pennsylvania senator contrasted himself not with his GOP rivals, but with President Obama. "I don't stand here as the conservative alternative to Mitt Romney," Santorum said. "I stand here as the conservative alternative to Barack Obama."

For Romney, the Minnesota loss was a double blow. After crushing John McCain in the 2008 caucus with 41 percent of the vote, Romney failed to break 20 percent Tuesday, even with big-name locals like former Gov. Tim Pawlenty pitching hard.

Santorum, who nearly camped out in Minnesota in recent days, spent much of that time portraying himself as an anti-Romney.

With contests in three states, Santorum spent part of Tuesday in Blaine at the National Sports Center, rousing more than 200 supporters.

"Don't settle for second best!" he exhorted, hours before the caucuses were to start.

Minnesota's caucus awards no delegates, but, along with Missouri, the win gave a serious boost to a candidate whose only other win was an eight-vote, delayed outcome in Iowa.

Paul had reason to be happy. The Texas congressman leapfrogged Romney and Gingrich, giving him momentum to continue.

Earlier in the evening, his supporters cheered as their hero appeared at a Maple Grove caucus.

"I am really enamored with him," said Dustin Darveaux, 32. "He speaks to my values."

A grinning Paul entered a caucus so packed that latecomers were forced to park nearly a mile away.

"Sounds like there are a lot of friends of freedom in this room," he said, smiling broadly.

But as the evening wore on, Paul found himself ceding ground to Santorum, even in areas where he was strong four years earlier.

"I guess I am kind of surprised, disheartened really," Micah Edel, 27, a graphic designer from Minneapolis, said at Paul's would-be victory party in Golden Valley.

At St. Paul's Highland Park Senior High School, Santorum supporter and former congressional candidate Edward Matthews said most of the delegates chosen by his precinct seemed to be Santorum supporters.

"Ron Paul's supporters are very organized and very committed ... but I didn't sense that he got any momentum that wasn't deserved," Matthews said.

Meanwhile, Romney had prepared observers for losses in Minnesota, Colorado and Missouri, the three states voting on Tuesday. "As our campaign has said from the outset, Mitt Romney is not going to win every contest," Matt Rhoades, Romney's campaign chief, said early in the day. Romney supporters got the message.

In Arden Hills, Greg Meyers arrived at Mounds View High School knowing it probably would not be a big night for his favorite, Romney.

"I'm probably going to be the only Mitt guy," said Meyers, chairman for House District 50B Republicans. "For a lot of people, he's not conservative enough."

He was right. Results in his suburban district: Santorum 204, Paul 118, Romney 85, Gingrich 35 and five write-ins. Four years ago, Romney won 44 percent of the vote there.

That story resonated in the Republican stronghold of Buffalo, Minn. While Romney swept that city in 2008, it was a Santorum rout in 2012.

In Buffalo, caucusgoer Don Tilus said Santorum was "level-headed."

"Some of the others have big money behind them and that isn't good," said the former union member.

Lori Sandahl joined Tilus in opting for Santorum. "I don't think he has what it takes to be president," she said of Romney.

Democrats, who had hammered Romney for months, prepared to continue the barrage. "Mitt Romney has a constituency of one -- his own political ambition," said DFL Party Chair Ken Martin.

DFLers, who turned out in record numbers for the 2008 caucuses, had a mellow caucus Tuesday.

"It's not like last time, when we had lines wrapped around the block," said Dr. Mary Pohl, a pediatrician, as she entered her St. Paul caucus.

Joining Pohl at a St. Paul caucus, Kate McGuire said she remains happy with Obama's job performance.

"I actually feel pretty good about him," she said. "If you stepped onto a train that was going downhill at 200 miles an hour, it's not so easy to make it go back uphill at 200 miles an hour. I'm not sure some people's expectations were reasonable or realistic."

Neither of Minnesota's two former presidential candidates were in the state Tuesday night. Pawlenty was in Kansas, talking about presidential politics. U.S. Rep. Michele Bachmann, who ended her own bid just a month ago, sent a letter to be read to delegates in advance of her bid for re-election in the Sixth District.

"As I continue my work in the House of Representatives ... I have not endorsed any candidate for president because my goal is to unite our party in pursuit of the mandatory goal of defeating the destructive Obama agenda," her letter said.

Rachel E. Stassen-Berger • Twitter: @rachelsb Star Tribune reporters Mike Kaszuba, Pat Doyle, Jim Ragsdale, Jennifer Brooks, Kevin Duchschere and Baird Helgeson contributed to this report.