Coats will face Democratic U.S. Rep. Brad Ellsworth in the general election in November to determine who will succeed Sen. Evan Bayh, who decided against seeking a third term.
The (Fort Wayne) Journal Gazette declared Coats the GOP primary winner. With 71 percent of the precincts counted, Coats had 40 percent with state Sen. Marlin Stutzman in second with 30 percent with John Hostettler, Don Bates and Richard Behney trailing.
Because of Bayh's late decision not to run, there was no Democratic primary for the seat and the party's state central committee will officially pick Ellsworth May 15, the Star said.
The 66-year-old Coats served in the U.S. House from 1980-88 and in the Senate from 1988-98.
WISH-TV, Indianapolis, reported U.S. Rep. Dan Burton, thought to have been vulnerable, held off challenger Luke Messer to win the 5th District Republican nomination.
The station also reported Indiana Secretary of State Todd Rokita outran a crowded Republican field in the 4th District where Republican Rep. Steve Buyer is retiring. Rokita will face Democrat David Sanders, a Purdue University biology professor.