Mitt Romney scored a hard-won victory in the Michigan primary and cruised to victory in Arizona Tuesday night, making him the clear frontrunner as the10-state Super Tuesday gauntlet approaches on March 6. 

"We didn't win by a lot, but we won by enough," Romney told cheering supporters in Michigan. 

The former Massachusetts governor also tweeted his delight — and his determination: "I take great pride in my Michigan roots, and am humbled to have received so much support here these past few weeks."

Romney capitalized on strong anti-illegal immigration attitudes among Arizona conservatives, carrying immigration voters by nearly 20 points, according to exit polls conducted by the Associated Press. While the economy remained the top issue in both states, 13 percent of Arizona Republican voters called illegal immigration the most important issue.

In a televised debate last week, Romney said he viewed Arizona's controversial efforts to pioneer an expanding role for local police in the enforcement of federal immigration law as a "model" for the country. Arizona Gov. Jan Brewer endorsed Romney on Sunday. 

In Michigan, by contrast, Romney struggled to compete with Rick Santorum on abortion, which 14 percent of GOP primary voters viewed as their most important issue. Santorum beat Romney among Michigan voters who viewed abortion as their top issue by 6-to-1.

Romney's double win owed most of all to voters who viewed the economy as the most important issue and those seeking the most electable candidate, exit polls indicated.

Playing to his experience in business, Romney adopted a new theme — "More jobs, less debt, smaller government" — and focused tightly on the economy, the biggest issue in the long-suffering manufacturing state of Michigan.

Romney also had more of Michigan's Republican establishment on his side, including Gov. Rick Snyder and a vast campaign structure, partly left over from his win in the 2008 primary.

Santorum, after storming into the state following a three-state sweep Feb. 7, slipped in the closing days by letting go the populist economic message that helped him emerge as the chief threat to Romney.

Romney fought hard against the challenge from Santorum, as he did in quelling the advance of former House Speaker Newt Gingrich in Florida.

The front-runner seized on comments Santorum made during an Arizona debate last week, when the former Pennsylvania senator said he had voted for legislation he disagreed with in order to support his party.

The comments allowed Romney to cast himself as an outsider from unpopular Washington and to cast Santorum as a Beltway creature.

While Romney's Tuesday night victories gave him in an edge over his GOP rivals, Santorum's strong showing underscores the lingering doubts conservatives have about the former governor.

Based on reporting by the Associated Press.

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino