DES MOINES (AFP) -- Mitt Romney is still the favorite to win the U.S. Republican presidential nomination, but a quick knock-out of his more conservative rivals seems out of reach after a near-draw in Iowa, experts said Wednesday.

“Iowa is a reminder that if Romney wins, it will be because he’s the last guy standing -- not because he has strong Republican support,” said Matt Dickinson, a political scientist at Middlebury College in Vermont.

The former Massachusetts governor and millionaire venture capitalist defeated Christian conservative Rick Santorum by a sliver of just eight votes, according to results announced by a party official early Wednesday.

Romney, who spent little time in this mostly rural heartland state until late December, practically writing it off, declared that both he and the former senator had had a “great victory” here and vowed to beat Obama in November elections.

Polls in New Hampshire, which votes second, on January 11, show Romney on track for a romp there.

But Iowa results, at 25 percent each, highlighted a year-long problem for Romney, who has had to fend off successive challenges from the right while being unable to push his support among Republicans above 30 percent.

“There really is a glass ceiling for Romney. He has spent money and time courting conservatives but he just can’t seem to bust through that,” said Bob Oldendick, a political scientist at the University of South Carolina.

“If you ask me who, after tonight, is the most likely person to win the nomination, I’d still have to say that’s Romney -- he has planned for a long-term battle and has a better organization,” he added.

Romney had made little secret that he hoped a strong finish in Iowa, a strong victory in New Hampshire, and another success in South Carolina, which could give him a lock on the nomination months before the general election.

But Oldendick, whose state votes January 21, said Iowa “really should give them (Romney’s advisers) some pause, that this is not going to be a quick knock-out, it’s going to be a long, drawn-out fight.”

Romney has portrayed himself as the best candidate to beat Obama in an election likely to be decided by middle-of-the-road voters, but he still faces doubts from Republicans about his conservative credentials.

“He still hasn’t captured the hearts of the GOP. He may have captured their mind, with electability, but he hasn’t captured their hearts,” said David Woodard, a political scientist at Clemson University in South Carolina.

“Santorum has reached the hearts and minds. He’s told them: ‘Yeah, the economy is a big problem but the culture is a bigger problem. I think it will play well here,” according to Woodard.

That’s not to say it’s a two-candidate race: Former House speaker Newt Gingrich heads into New Hampshire and South Carolina eager to exact payback for attacks ads from Romney allies that doomed him to fourth place in Iowa.

Veteran Representative Ron Paul, a small-government champion also known for his fierce opposition to foreign aid and military intervention, came in third here, and his devout following could help him play spoiler elsewhere.

But Romney benefits from seeing more Republicans, like those aligned with the ultra-conservative Tea Party, fractured among several rivals, but if they “decide on an anti-Romney alternative, Romney is in trouble,” Dickinson said.

“Gingrich and Paul are going to go after Romney here. That will potentially be quite damaging,” said Linda Fowler, a politics expert at Dartmouth College.

“Romney still looks strong in the polls in New Hampshire. But it is clear from Iowa that he still hasn’t made the sale with primary voters. The message from Iowa is he still has to work for it,” she said.