Michigan handed Mitt Romney his first major win in the Republican presidential primary contest yesterday, pushing the former Massachusetts governor to the top in the still-meager tally of delegates awarded in the race to win the party’s nomination.

Mr. Romney’s victory, which came by a decisive nine-point margin, left the Republicans with a splintered field where no candidate has emerged as an obvious frontrunner and no clear pecking order has been established among the contenders.

With 93% of Michigan precincts reporting, Mr. Romney had 324,409 votes, or 39%; Senator McCain of Arizona had 246,818, or 30%, and Michael Huckabee had 133,881, or 16%.

Mayor Giuliani lagged far behind in Michigan, coming in sixth place with 23,618 votes, or 3%. That put him behind both Rep. Ron Paul, who had 52,181 votes, or 6%, and Fred Thompson, with 30,759, or 4%, and just ahead of uncommitted, which scored 16,871 votes, or 2%.

“Tonight marks the beginning of a comeback — a comeback for America,” Mr. Romney told cheering supporters in Southfield, Mich., a suburb of Detroit. His speech breached the usual election night protocol by beginning while Mr. McCain was still in the process of conceding. The victor also wasted little time in characterizing the win as a message that Washington veterans, such as the Arizona senator, are ill-suited to end the political gridlock and runaway spending in the capital.

“This is a victory of optimism over Washington-style pessimism,” Mr. Romney said, alluding to Mr. McCain’s statement that many of Michigan’s lost automotive industry jobs were probably gone for good. “I will never accept defeat for any industry here in America. We will fight for every job,” Mr. Romney vowed.

Mr. Romney’s rivals, sensing their likely losses in Michigan, left the state and took in the returns from rallies in South Carolina, where Republican voters go to the polls on Saturday.

Mr. McCain told supporters in Charleston that he had no regrets about the message he gave to Michigan voters, even if they did not particularly like it. “We have no cause to be discouraged or to second guess what we might have done differently,” the Arizona senator said. “We did what we always do. We went to Michigan and we told the people the truth. We always tell them the truth.”

Much of Mr. Romney’s campaign message in Michigan centered on the Detroit-born candidate’s personal ties to the state and his family’s role in the automobile business. His father, George, served as president of the American Motors Corp. and was later a popular Michigan governor.

In their comments last night, Mr. Romney’s rivals congratulated him on his victory, but went on to dismiss his win in the state as an aberration attributable to his roots there. “His campaign worked hard and effectively to make sure that … Michigan voters welcomed their native son with their support. Michigan voters were good to the native son and I understand that,” Mr. McCain said.

The third-place finisher, Mr. Huckabee, credited Mr. Romney for running a “great campaign” in Michigan, but quickly added, “Of course, he had a great base there.” The former Arkansas governor suggested Mr. Romney’s financial advantages helped drive the vote in the Wolverine State. “Electing a president is not just about how much money a candidate has,” Mr. Huckabee said, claiming he was outspent 50-to-1.

Speaking to backers in Lexington, S.C., Mr. Huckabee stressed the open nature of the Republican nominating contest. “I won Iowa. John McCain won New Hampshire. Mitt Romney won Michigan. And we’re going to win South Carolina. We put a flag in the ground here,” he said.

Mr. Romney seemed to benefit from Michigan voters’ intense focus on the economy. Exit polls conducted by television networks and the Associated Press indicated that 55% of voters in the Republican primary considered the economy the top issue facing America, about double the 26% in Iowa and 31% in New Hampshire who picked that as their main concern.

As in New Hampshire, Mr. Romney fared better with self-described Republicans in Michigan, defeating Mr. McCain 41% to 27%, while the Arizona senator did somewhat better with independents, beating the former Massachusetts governor 35% to 29%, according to the exit poll data. Only about a quarter of those who voted in the Republican contest were independents, a turnout that undercut Mr. McCain. About 7% of Republican primary voters called themselves Democrats. In Michigan, any voter can vote in any party primary.

The Democratic contest was essentially a nonfactor in Michigan. Senator Clinton and Rep. Dennis Kucinich of Ohio were the only notable candidates on the ballot, after Senator Obama and John Edwards pulled their names off. The Democratic National Committee denied the state all 156 delegates and essentially banned campaigning in the state because it moved its primary to a date earlier than that allowed under party rules.

The Republican Party imposed a lesser penalty, stripping the state of half of its normal allotment of 60 delegates.

In the past, such delegate sanctions have been dropped prior to the party conventions, but there is no assurance that will happen this time, particularly if the nominating contests are close.

Senator Clinton won handily on the Democratic side, pulling in 302,611 votes, or 55%, while the choice of “uncommitted” came in at 216,925, or 40%, with 93% of precincts reporting. Mr. Kucinich had 20,478 votes, or 4%.

Exit polls indicated that Mrs. Clinton fared poorly among African Americans, who may have been casting protest votes against what some viewed as racially tinged appeals in a recent flurry of charges and counter-charges between her supporters and Mr. Obama.

However, it was difficult to draw conclusions from the Democratic exit surveys in Michigan because of widespread news coverage stating that the Democratic vote was irrelevant because of the timing dispute with the national party.

Such publicity may have led casual and rank-and-file voters to stay home, while failing to discourage, and perhaps even provoking, voters seeking to send a message to Mrs. Clinton or to state Democratic Party leaders whose maneuvering with the calendar may have effectively disenfranchised Michigan Democrats in one of the most hotly contested primaries in recent decades.