Rick Santorum won Republican presidential primaries in Alabama and Mississippi, propelling his candidacy and wrecking Mitt Romney‘s hopes for a game-changing Southern breakthrough.

While the returns were incomplete, Newt Gingrich was running second ahead of Romney in both states.

Santorum, speaking in Louisiana, took a rhetorical swipe at Romney, the front-runner who has depicted himself as the inevitable GOP nominee. The former Pennsylvania senator predicted he would win the nomination.

“He spent a whole lot of money against me, for being inevitable,” Santorum said of Romney. He added that “all the establishment” of the Republican Party was “on the other side of this race.”

“We are going to win this nomination,” Santorum said. “If we nominate a conservative, we will defeat Barack Obama and set this country back on the right track.”

With most precincts counted in Alabama, Santorum had nearly 35% of the vote.

In Mississippi, Santorum had a small lead and 33% of the vote with nearly all precincts counted.

By Evan Vucci, APMitt Romney speaks at a campaign event in Liberty, Mo., on Tuesday.

Santorum was eager for Gingrich to be swept aside, arguing that he could defeat Romney in later primaries if the race boiled down to two main candidates.

Gingrich, in Birmingham, Ala., congratulated Santorum and said the outcome showed Romney was far from a sure thing to win the nomination.

“If you’re the front-runner and you keep coming in third, you’re not much of a front-runner,” the former House speaker said.

Gingrich said he would continue his campaign and that the proportional allocation of delegates means, with his share of the votes, “we’re going to leave Alabama and Mississippi with substantial numbers of delegates.”

By David Goldman, APNewt Gingrich speaks at a primary night rally in Birmingham, Ala., on Tuesday, as his wife, Callista, applauds.

The fourth candidate, Rep. Ron Paul of Texas, did not seriously contest either state and was running a distant fourth in both, his percentages in the single digits.

The other three hopefuls competed heavily in the twoDeep South states. Romney and his allies outspent the rival campaigns.

Santorum picked up the vote of Alabama Gov. Robert Bentley, who said through spokesman Jeremy King that he considered Santorum as “the most conservative candidate in the Republican presidential race.”

Romney’s team had hoped that a victory in Alabama or Mississippi — which the former Massachusetts governor acknowledged amounted to an “away game” for him — would go a long way toward solidifying his claim as the leader for the GOP nomination. Santorum had hoped to elbow Gingrich aside and emerge as the leading alternative to Romney.

There were 47 nominating delegates at stake in Alabama and 37 in Mississippi.

Hawaii was holding caucuses with 17 delegates at stake. Tiny and remote American Samoa, with six GOP delegates, also was holding a caucus.

Evangelical voters were a major factor in both states. A survey of voters as they were leaving their polling places found 80% in Alabama and Mississippi described themselves as evangelical or born-again Christians. Santorum was the leader among those voters in both states, as he had been in Tennessee and Oklahoma, among other recent contests he won in the region.

Voters sampled in the exit polls were overwhelmingly conservative in both states, and in Mississippi, 80% described themselves as dissatisfied or angry with the federal government. Eight of 10 GOP voters in Alabama said they would definitely vote for the Republican candidate against Obama, no matter who is the nominee.

Romney went into the contests with 454 of the 1,144 delegates needed to win the nomination, according to a tally by the Associated Press. Santorum had 217, Gingrich 107 and Paul 47.