Republican Mitt Romney's victory in Michigan on Tuesday kept his presidential campaign alive, put the brakes on rival John McCain and left their party still with no clear White House favourite.

After three big contests in the race to determine which Republican will face the Democrats' choice in the November election, there have been three winners: Mike Huckabee in Iowa, John McCain in New Hampshire and now, Romney in Michigan.

Romney had built his campaign on a strategy of winning Iowa and New Hampshire. After losing both, the former Massachusetts governor had to win his birth state of Michigan to retain credibility as a candidate. Anything less than victory could have doomed him to irrelevance, despite his ability to spend millions of his own dollars to stay in the race.

Now he can claim momentum heading into the South Carolina contest on Saturday and Florida on January 29. Most importantly, 22 states will vote on "Super Tuesday," February 5.

Both parties had expected to crown their nominees that night but some strategists now believe the race in either or both parties could continue beyond Super Tuesday.

"Tonight marks the beginning of a comeback -- a comeback for America," a relieved Romney said at a victory rally in Southfield, Michigan.

The Michigan campaign was dominated by economic concerns. The state where the auto industry once was king has a higher jobless rate than any other U.S. state, 7.4 percent in November, but Romney said he could bring some of those lost jobs back and ease government restrictions on the automakers.

McCain's message in Michigan was the sort of "straight talk" for which he is famous: Some of those lost jobs will not be coming back, and those workers must be retrained for new, high-tech jobs.

Romney turned that around on McCain, vowing to help the auto industry and said the Arizona senator was offering a pessimistic message to be expected from a Washington insider.

"Tonight is a victory of optimism over Washington-style pessimism," Romney said on Tuesday night.

McCain told supporters in Charleston he had no regrets about his Michigan strategy.

"We fell a little short tonight. But we have no cause to be discouraged or to second guess what we might have done differently. We did what we always try to do: We went to Michigan and told people the truth," he said.

STRATEGIC LIMITS

The loss showed McCain the limits of his strategy of appealing to independents and moderate Republicans. Exit polls cited by the Fox News Channel showed that while McCain attracted much support from independents, the die-hard Republican faithful turned out mostly for Romney.

A win in Michigan would have made McCain, 71, the clear Republican front-runner. But he remains a potent candidate, leading the polls in South Carolina and Florida.

"It hurts McCain's momentum," said Merle Black, a political science professor at Emory University in Atlanta. "It would have helped him if he had been able to put two consecutive victories together."

"But McCain is still very competitive in South Carolina and Florida. So McCain will survive this loss, and it clearly indicates there is no consensus among Republicans about their nominee."

McCain, Romney, former Arkansas Gov. Mike Huckabee and former Tennessee Sen. Fred Thompson now turn their attention to South Carolina, the first state in the South to vote in the 2008 race.

"The winner in South Carolina has the chance to catch the momentum and carry this through Super Tuesday" and become the party's nominee, said Republican strategist Scott Reed.

Huckabee, the ordained Baptist preacher who won in Iowa with strong support from evangelical Christians, hopes to attract the same type of support in South Carolina.

But exit polls showed Huckabee splitting the evangelical vote in Michigan with Romney, suggesting Huckabee does not have a lock on that constituency.

Huckabee predicted to Fox News he will win South Carolina.

Besides Romney, the happiest candidate on Tuesday night might have been former New York Mayor Rudy Giuliani, who has concentrated on winning Florida.

Romney's win meant Giuliani still has a chance to win Florida and swing into February 5 with momentum.

"It's clear after tonight that while the race remains fluid and competitive, our strategy remains on track," said Giuliani senior adviser Tony Carbonetti.