ABC projected Rick Santorum would win the Albama and Mississippi primaries, giving the former Pennsylvania senator high-stakes victories in key Southern contests today.
Mitt Romney, who still holds a commanding delegate lead for the nomination, trailed in third place behind Newt Gingrich in both races, with majorites of precincts reporting.
Santorum's victories came after a week of polls that showed the three challengers running virtually neck-and-neck in both states, which award delegates on a proportional basis.
Late Tuesday night Romney had 471 delegates, Santorum had 238 and Gingrich had 126 total delegates. A candidate needs 1,144 to secure the nomination.
But the Alabama and Mississippi wins will provide a boost to Santorum, even though he will still be well behind in the race for delegates. Before polls closed today, Romney said Santorum was "at the desperate end" of his campaign -- a prediction that may prove premature after today's results.
The candidates did not stick around for results.
"We did it again," Santorum declared at an event in Louisiana. He said that despite Romney's deep campaign pockets, he has won in the Midwest and South and is forcing the Romney campaign back on its heels. He heads to Puerto Rico Wednesday to campaign.
Romney spent the night in Missouri, which holds a state caucus Saturday. Santorum won a non-binding primary there in February.
In a paper statement, he pointed to his continuing delegate lead.
"I am pleased that we will be increasing our delegate count in a very substantial way after tonight," he said. "Ann and I made a lot of new friends in Alabama and Mississippi and we look forward to campaigning in those states in the general election."
Gingrich stayed in Alabama to watch the results, which he said dealt a blow to Romney.
"If you're the front runner and you keep coming in third, you're not much of a front-runner," Gingrich said.
The large proportion of evangelical Christian voters in the two states was not fertile ground for Romney, but the former Massachusetts governor put together a strong organization, particularly in Mississippi.
According to an ABC News analysis of exit poll results in Alabama, strongly conservative voters gravitated toward Santorum and Gingrich -- together the two candidates claimed nearly eight in 10 of them.
In Mississippi, however evangelical voters, not typically Romney's strong suit, were trending in his direction -- 32 percent of members of that group supported him, according to exit polls.
Four in 10 voters said electability was their most important criteria when choosing a candidate at the ballot box on Tuesday, which may have helped keep Romney competitive.
All three candidates swept through the two Southern strongholds in recent days, with Romney declaring his love for "cheesy grits" and the term "y'all." He was aided in his quest to win the Mississippi primary by a political organization helmed by two members of former Mississippi Gov. Haley Barbour's family. Barbour's nephews, Henry and Austin, led a team of field organizers and advisers that ran Romney's ground game there.
On his campaign plane in Missouri today, Romney said the primaries were "all about getting delegates."
"If the polls are anywhere near correct, we'll end up with, I don't know, a third of the delegates," he told reporters aboard a flight from St. Louis to Kansas City. "And if that's the case, why that inches us closer to that magic number."