Mitt Romney won at least three primaries as he reached for a decisive advantage in the Republican presidential race on Super Tuesday, the busiest day of the chaotic campaign to choose a rival to President Barack Obama.

The first returns produced few surprises as Romney, as expected, won Virginia, Massachusetts and Vermont, while his main rival, Rick Santorum, took Tennessee and Oklahoma. Newt Gingrich won his home state of Georgia.

Less predictable was the marquee battle in Ohio, where, with 36 percent of precincts reporting, Santorum had 39 percent and Romney 36 percent.

With contests in 10 states, the day marked a key point in the Republican race. Romney, the clear, yet battered, front-runner, looked to prove his appeal across the country and demonstrate that the party's conservative base, long wary of the former Massachusetts governor, is finally rallying behind his candidacy.

Santorum, a former U.S. senator, had to prove that he still has a clear shot at the nomination, overcoming Romney's momentum from recent wins and his advantage in money and organization. He also needed to keep Romney from building a runaway lead in the tally of delegates who will ultimately determine the Republican nominee.

Gingrich, who has twice soared to the top of the field only to fade, needed the win in Georgia to keep his campaign alive. Despite the victory, Gingrich, a former speaker of the House of Representatives who represented a Georgia district for two decades, remains a longshot for the nomination, but his continued candidacy could ultimately help Romney by siphoning conservative votes from Santorum.

At stake Tuesday were 419 delegates, more than a third of the 1,144 delegates needed to win the nomination at the party national convention in late August in Tampa, Florida. With Tuesday's results coming in, Romney was leading with 273 to Santorum's 108, according to Associated Press projections. By winning at least 29 delegates in Georgia, Gingrich now has 62. Congressman Ron Paul has 25.

Romney had been almost certain to win in Virginia, where he shared the ballot with only Paul, after neither Santorum nor Gingrich met filing requirements. He had been favored to win in the two northeastern states, Vermont and Massachusetts, considered his home state.

Santorum's wins in Tennessee and Oklahoma reflected his appeal to evangelicals, an important part of the Republican base in the South. He has contrasted his steadfast stances on social issues, such as opposition to abortion and gay marriage, with Romney's shifting positions.

"We're going to win a few. We're going to lose a few. But as it looks right now, we're going to get a couple of gold medals and a whole passel of silver," Santorum told cheering supporters in Ohio.

Ohio, a heavily populated Midwestern industrial state, was a test of the strength of Santorum, who is from neighboring Pennsylvania. Ohio is bound to be critical in the November general election, which is essentially a series of simultaneous state-by-state contests.

Obama's hopes for re-election once seemed dim because of the weak U.S. economy. But polls show his prospects have improved in recent months, as the economy has strengthened, unemployment has slowly declined and Republicans have ripped into one another in a tumultuous nominating campaign.

Obama stepped into the Republican race by holding a news conference on Tuesday. He dismissed their almost-constant criticism of his foreign policy efforts and accused Republicans of "beating the drums of war" in Iran. "Those folks don't have a lot of responsibilities. They're not commander in chief," he said.

Asked what he had to say to Romney in response to the Republican's harsh criticism, he responded with a big smile, "Good luck tonight."

Romney has campaigned as the candidate with the best prospects of beating Obama. He is seen as more moderate than his main rivals, giving him better prospects for winning over centrist, independent voters who often swing U.S. presidential races.

But that perceived moderation has made him vulnerable to attacks by Gingrich and Santorum.

Romney's campaign was staggered when Santorum won a pair of caucuses in Colorado and Minnesota and a nonbinding Missouri primary on Feb. 7. But Romney entered Super Tuesday on a winning streak. He captured the Washington state caucuses last Saturday, days after winning a little-contested primary in Arizona and a hard-fought one in his home state of Michigan. He narrowly won the Maine caucuses earlier in February.

Other states voting Tuesday were North Dakota, Idaho and Alaska, all of which had caucuses.