UPDATE: Romney sweeps to double victory in Ariz., Mich.

WASHINGTON (AP)

Mitt Romney scored a hard-won, home state triumph in Michigan and powered to victory in Arizona Tuesday night, gaining a two-state primary sweep over Rick Santorum and precious momentum in the most turbulent Republican presidential race in a generation.

Two other candidates, Newt Gingrich and Ron Paul, made little effort in either state, pointing instead to next week's 10-state collection of Super Tuesday primaries and caucuses.

Romney's Arizona triumph came in a race that was scarcely contested, and he pocketed all of the 29 Republican National Convention delegates at stake.

Michigan was as different as could be - a hard-fought and expensive race in Romney's home state that he could ill afford to lose and Santorum made every effort to win.

Returns from 34 percent of Michigan's precincts showed Romney at 41 percent and Santorum at 38 percent. Paul was winning 12 percent of the vote to 6 percent for Gingrich.

Arizona awarded all 29 of its delegates to the winner of the statewide vote.

In Michigan, by contrast, 30 delegates were apportioned according to the popular vote. Two were set aside for the winner of each of the state's 14 congressional districts. The remaining two delegates were likely to be divided between the top finishers in the statewide vote.