Mitt Romney scored his first major primary victory Tuesday, a desperately needed win in his native Michigan that gave his weakened presidential candidacy new life. It set the stage for a wide-open Republican showdown in South Carolina in just four days. Three GOP candidates now have won in the first four states to vote in the 2008 primary season, roiling a nomination fight that lacks a clear favorite as the race moves south for the first time. The former Massachusetts governor defeated John McCain, the Arizona senator who was hoping that independents and Democrats would join Republicans to help him repeat his 2000 triumph here. Mike Huckabee, the former Arkansas governor, trailed in third, and former Tennessee Sen. Fred Thompson is making a last stand in South Carolina. "It's a victory of optimism over Washington-style pessimism," Romney said in an Associated Press telephone interview from Southfield, Mich., echoing his campaign speeches and taking a poke at McCain, the four-term senator he beat. "Now on to South Carolina, Nevada, Florida." Minimizing the significance of Tuesday's vote, McCain said he had called Romney to congratulate him "that Michigan welcomed their native son with their support." "Starting tomorrow, we're going to win South Carolina, and we're going to go on and win the nomination," McCain declared, also in an AP interview from Charleston, S.C. Huckabee, too, already campaigning in the next primary state, predicted in Lexington, S.C., he would "put a flag in the ground here Saturday." He also jabbed at Romney, who has poured at least $20 million of his personal fortune into his bid: "We need to prove that electing a president is not just about how much money a candidate has." In Michigan, with most precincts reporting, Romney had 39 percent of the vote, McCain had 30 percent and Huckabee 16 percent. No other Republican fared better than single digits. Previously, Huckabee had won leadoff Iowa, and McCain had taken New Hampshire. Romney won scarcely contested Wyoming. Hillary Rodham Clinton was the only top contender on the Democratic ballot Tuesday. With most precincts counted, she had 56 percent of the vote to 39 percent for uncommitted delegates to the Democratic National Convention. Romney's ties to Michigan proved beneficial. Four in 10 voters said his roots factored into their decisions, and 58 percent of that group backed him, according to preliminary results from surveys of voters as they left their polling places, taken for The AP and the networks. He also led among voters who said the economy (42 percent) and illegal immigration (39 percent) were their most important issues, and won the most Republicans (41 percent), conservatives (41 percent), evangelicals (34 percent) and voters looking for a candidate with experience (52 percent) or shared their values (37 percent). McCain had an edge with those who wanted an authentic president (43 percent), and he won among moderates (40 percent), independents (35 percent) and Democrats. But fewer non-Republican voters participated in the GOP primary this year than in 2000 when those voters helped him beat George W. Bush. Independents and Democrats accounted for roughly one-third of the vote, compared with about one half eight years ago. Romney had a slight edge over McCain as the candidate likeliest to bring needed change, 32 percent to 28 percent. The economy proved the most important issue for Republicans in Michigan, the state with the highest unemployment rate in the nation and an ailing auto industry. Given four choices, 55 percent of Michigan Republican primary voters picked the economy as the most important issue, while 17 percent picked Iraq, 13 percent immigration and 11 percent terrorism. A mere 20 percent or less of eligible voters were expected to show up at polling stations across frigid and snowy Michigan, the turnout depressed in part by the Democratic race of little to no consequence. For Republicans, the stakes varied. Of the three candidates competing hard here, Romney needed a Michigan victory the most to invigorate a campaign crippled by searing losses in Iowa and New Hampshire. He was the only one who watched the voting returns in Michigan; his top Michigan opponents, McCain and Huckabee, campaigned in the state earlier in the day but left by afternoon to plant themselves in next-up South Carolina. Up for grabs in Michigan were 30 Republican delegates. Romney campaigned in the state far more than his rivals and spent more than $2 million in TV ads in Michigan, nearly three times what McCain did, according to an analysis of presidential advertising by the nonpartisan Michigan Campaign Finance Network. McCain paid for more than $740,00 in ads and Huckabee spent more than $480,000. Feeling optimistic in the run-up to the Michigan voting, Romney went back on the air with TV ads in South Carolina after a brief hiatus. A muddle from the start, the GOP race has grown ever more fluid as the first states voted over the past two weeks. Romney was second to Huckabee in the Iowa caucuses and to McCain in New Hampshire's primary while Huckabee dropped to third. Thompson is camping out in South Carolina looking for his first win. Rudy Giuliani is doing the same in Florida, which votes Jan. 29. The former New York mayor got only 3 percent of the Michigan vote, trailing Thompson and Texas Rep. Ron Paul as well as the top three, and he hasn't fared better than fourth in any of the states so far. Yet, the fractured GOP field plays into his strategy of lying in wait - and making his move - in Florida in the run-up to Feb. 5 when some two dozen states vote. Romney was born and raised in Michigan, and his late father, George, was head of American Motors and a three-term governor in the 1960s. The younger Romney announced his presidential candidacy in the state a year ago. McCain had a built-in advantage of his own. He won the state's primary eight years ago on the strength of independent and Democratic-crossover voters, and he still had a network of hard-core backers. Six months after his campaign nearly collapsed, he now leads national polls. Huckabee, an ordained Southern Baptist minister, had hoped to stage a surprise finish with the support of Christian evangelicals who live in the more conservative, western part of the state. With his populist pitch, Huckabee also wanted to do well in Reagan Republican country outside of Detroit. The economy dominated the weeklong Michigan campaign. The state has been reeling from the U.S. auto industry's downturn and has the nation's highest unemployment rate at 7.4 percent. Michigan doesn't typically hold its primary until February but state party officials scheduled it earlier to try to give the state more say in picking a president. The Republican National Committee objected and cut the number of Michigan delegates to the national convention by half as punishment while the Democratic National Committee stripped the state of all 156 delegates to its national convention, including 28 superdelegates who would not have been bound by the outcome of the primary.