Detroit (CNN) — Mitt Romney will win Tuesday’s Arizona primary, CNN projected based on exit polls, and he took an early lead over rival Rick Santorum in Michigan, a key contest in the Republican race for a candidate to run against President Barack Obama in November.

The victory in Arizona, where exit polls showed Romney getting 43% to 28% for Santorum, gives the former Massachusetts governor all of the state’s 29 delegates in the winner-takes-all primary. Trailing well back were the other two GOP contenders — Newt Gingrich and Texas Rep. Ron Paul.

In Michigan, Romney was ahead with 41% to 38% for Santorum, 11% for Paul and 7% for Gingrich with 25% of unofficial returns counted. The state’s 30 delegates will be allocated on a proportional basis.

Romney needs to win Michigan, where he grew up when his father was governor, to assert his ability to overcome the conservative challenge from Santorum.

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