U.S. presidential candidate Mitt Romney on Tuesday bagged double wins in primary battles in Arizona and Michigan, the state where he grew up.

U.S. presidential candidate Mitt Romney on Tuesday bagged double wins in primary battles in Arizona and Michigan, the state where he grew up. [Agencies]

According to projections by major U.S. TV networks, Romney, the former Massachusetts governor, won easily in Arizona, defeating main rival Rick Santorum, the former Pennsylvania senator, with double-digit edge.

But the main fight of the day was centered around Michigan, a state which was supposed to be Romney's backyard, where his father served as a popular governor. Poll results before the primary showed him in dead heat with Santorum, prompting pundits to speculate what a loss in his childhood home meant to the candidate and to the GOP race.

With about 88 percent of votes counted, Romney led with 41 percent of the vote, followed by Santorum with 38 percent, U.S. broadcasters projected while the ballots were still being calculated.

Texas congressman Ron Paul finished third with 12 percent of the vote. Former House Speaker Newt Gingrich, who mostly skipped the state, came in last at 7 percent.

Santorum, who was campaigning in Michigan, told supporters that a month ago, "they didn't know who we are, but they do now," referring to his close second place finish. He called Romney to concede Michigan before going before the supporters.

Romney, who spoke later, looked to his prospects in the campaign and vowed he would defeat President Barack Obama should he becomes nominee, promising to bring about a better economy.

The victory was critical for Romney going into the Super Tuesday contest in March, when 10 states will hold primary battles. A defeat in his home state -- even by the slightest margin -- would have been devastating to his campaign.

Romney's standing before the Michigan primary was weakened by his gaffes, his remarks last week that his wife Ann drove "a couple of Cadillacs" highlighted the candidate's personal wealth. His reference during a visit to the Daytona 500 to being friends with NASCAR team owners had perpetuated his rich man image. Romney admitted those remarks damaged his campaign.

The campaign also took a nasty turn after the Santorum campaign began urging Democratic voters to turn out at the Michigan polls and vote against Romney, blasting Romney for his support for Wall Street bailout, but opposition to auto bailouts.

But the lead Santorum had in Michigan collapsed after his poor performance in a debate last night, and the controversy surrounding his remarks on contraceptives and women's issues. Exit polls suggest he performed badly among working class women in Michigan.