WASHINGTON - Tea party favorite Chris McDaniel and six-term Sen. Thad Cochran dueled inconclusively at close quarters in Mississippi's primary election Tuesday night, an epic struggle in a party deeply divided along ideological lines. GOP governors in South Dakota, Alabama and Iowa all coasted to renomination.

Senate hopeful Joni Ernst, a state senator, overwhelmed a fistful of Republican rivals in Iowa after uniting rival wings of the party and will challenge Rep. Bruce Braley this fall for a Senate seat long in Democratic hands.

In a third Senate race on the busiest night of the primary season, former Gov. Mike Rounds won the Republican nomination in South Dakota - and instantly became the favorite to pick up a seat for the GOP in its drive to capture the six the party needs to capture a majority this fall.

Five states picked candidates for governor, including California, where Democrat Jerry Brown cruised to renomination to a fourth term.

The marquee contest of the night was in Mississippi, where Cochran, 76, and the 41-year-old McDaniel remained locked in a close, uncallable race as the vote count mounted. Returns from 98 percent of the state's precincts showed the challenger narrowly ahead in a three-way race, but just below the 50 percent threshold needed to avoid a June 24 runoff.

"People of this country were somehow awakened and we've been asleep for far too long," McDaniel told supporters as the results came in.

Rep. Gregg Harper, who had campaigned with Cochran, told the senator's supporters, "It's looking like a run-off."

Officials said the vote tally did not include provisional ballots, at least some of them cast as a result of the state's new voter ID law. Those voters have five days to furnish proof of residence. An official canvass could take longer, until June 13.

Dozens of nomination races for House seats dotted the ballot, and including 38 in California's open primary system, which awarded spots on the November ballot to the two top vote-getters regardless of party.

The Senate contest between Cochran and McDaniel in Mississippi drew top billing, a costly and heated race between a pillar of the GOP establishment who has helped funnel millions of dollars to his state and a younger state lawmaker who drew backing from tea party groups and former Republican vice presidential candidate Sarah Palin. The campaign took a turn toward the sensational when four men, all McDaniel supporters, were arrested and charged with surreptitiously taking photographs of the senator's 72-year-old wife, who suffers from dementia and has long lived in a nursing home.

One black group of Cochran supporters, "All Citizens for Mississippi," advertised in two black newspapers and handed out flyers in the race's final days as they appealed to traditionally Democratic voters to extend his career.

Vicksburg Mayor George Flaggs, a black Democrat who served for 26 years in the state Legislature, said he was supporting the white, Republican incumbent. He said the senator has secured federal funding for a U.S. Army Corps of Engineers research station in his city, adding, "It is incumbent for me to vote for Thad."

The race was arguably the year's last good chance for the tea party wing of the party to topple an establishment favorite in a Senate primary, following losses in Texas, North Carolina, Georgia and Kentucky.

The impact of the race seemed less in the national battle for control of the Senate. Former Rep. Travis Childers captured the nomination to oppose the winner of the Cochran-McDaniel race in a state that last elected a Democratic senator in 1982.

The national stakes were higher in Iowa, where Democratic Sen. Tom Harkin's retirement created an open seat that Democrat Braley, a fourth-term lawmaker, seeks to fill - as does Ernst.

She was able to transcend many of the intra-party divisions that flared in other races, gathering business groups, abortion foes, the Senate Conservatives Fund and the U.S. Chamber of Commerce - groups not always on the same side in a season of struggle for the GOP.