With 57 percent of the state's precincts reporting, the Milwaukee Journal Sentinel said Barrett, the mayor of Milwaukee, would be the Democratic nominee. He had 56 percent (191,214 votes). Former Dane County Executive Kathleen Falk was second with 36 percent (124,685 votes), followed by state Sen. Kathleen Vinehout at 4 percent (13,692), Secretary of State Doug La Follette at 3 percent (10,852) and Gladys Huber at 1 percent (2,761).
Barrett and Walker will square off in the June 5 general election.
Walker easily fended off a challenge in the Republican primary by Arthur Kohl-Riggs. Walker had 97 percent of the vote (381,587) to 3 percent (10,729) for Kohl-Riggs.
Officials had projected a 30 percent to 35 percent turnout -- about 1.5 million voters -- which would be short of the record 38.9 percent voting in a 1952 primary, the highest primary turnout on record in Wisconsin, state Government Accountability Board said.
The state has an open-primary system that didn't require voters to declare a party affiliation. That created the possibility Republicans could have cast ballots for Falk, a former Dane County executive, to derail Barrett's bid, The Christian Science Monitor noted.
Polls had indicated Falk was the weaker candidate against Walker, who was polling in a dead heat against Walker heading into the balloting.
Marquette University polling director Charles Franklin told the Monitor polls indicated Republicans would likely not "cause mischief in the Democratic primary."
Independent voters were expected to be key, with 36 percent of likely voters identifying themselves as independent, a poll conducted by Marquette University Law School in Milwaukee indicated.
Walker, who has battled public employee unions since taking office last year, framed the recall election as damaging to the state's economic health, particularly job creation.
He told the Journal Sentinel last week if he loses, it will open the door to "recall ping-pong."
"It will go back and forth. I don't think that's just bad for elections -- it's bad for jobs," he said.
Wisconsin lost 23,900 jobs between March 2011 and March 2012, data released last month by the U.S. Bureau of Labor Statistics indicated.
By comparison, no other U.S. state lost more than 3,500 jobs.
Walker was one of six Wisconsin Republicans facing recalls Tuesday. The others include Lt. Gov. Rebecca Kleefisch and four GOP state senators.