Romney defeated his principal rival John McCain by winning a clear plurality of Republicans and conservatives, who turned out in greater numbers than they had in the 2000 primary, which McCain won.

“Tonight marks the beginning of a comeback,” Romney said in declaring victory at a hotel rally in Southfield. “Tonight is a victory of optimism over Washington-style pessimism.”

Romney needed a victory in Michigan to save his candidacy after finishing second to McCain in New Hampshire and to Mike Huckabee in Iowa. Huckabee finished third in Michigan.

With 97 per cent of the electoral precincts reporting, Romney had 39 per cent of the vote, compared with 30 per cent for McCain and 16 per cent for Huckabee. Ron Paul, the antiwar congressman from Texas, came in fourth with 6 per cent of the vote.

Romney’s victory here means three different Republican candidates have won each of the first three major contests. The race moves to South Carolina and Nevada this weekend with no clear front-runner and two credible candidates, Rudolph W Giuliani and former Fred D Thompson, yet to seriously contest a state.

Katon Dawson, the Republican chairman in South Carolina, declared the race for the party’s nomination wide open.

In conceding defeat on Tuesday, McCain congratulated Romney, but said he would be direct about the problems facing the economy.

“We did what we always try to do — we went to Michigan and we told people the truth,” McCain said. “I am as committed now as I have ever been to making sure that no state, whether it’s Michigan or South Carolina or anywhere in this blessed country, is left behind in the global economy.”

A senior McCain advisor said the Michigan result meant that McCain had to win in South Carolina to assert a dominance of the field. If he does not, this advisor said, it makes it more likely that Republicans will fail to coalesce around a candidate even after 21 states hold their nominating contests on February 5.

The Michigan results showed much of Romney’s support came from the three-county Detroit metropolitan area, home of many well-off Republicans and where the Romney name is better known. Romney’s father, George, was governor of Michigan from 1963 to 1969, and he repeatedly highlighted his Michigan roots in campaign appearances.

The exit polls, conducted by Edison/Mitofsky for the television networks and The Associated Press, also found that Romney did well among those who decided in the last day or two, validating his strategy of saturating the state over the past five days with advertising and personal appearances.

Hillary Clinton, the only major Democratic candidate whose name was on the ballot in Michigan, was the winner on the Democratic side. Barack Obama and John Edwards withdrew their names at the request of the national Democratic Party, which penalised Michigan with the loss of its convention delegates because the early date of its primary violated party rules.