Hogan released an Internet ad calling the lieutenant governor "the most incompetent man in Maryland" and vowed to make the campaign a referendum on Gov. Martin O'Malley's tenure.
Brown shot back that he would make the campaign a referendum on the "failed administration" of Maryland's last Republican governor, Robert L. Ehrlich Jr., in whose Cabinet Hogan served.
"It's disappointing that he would choose a negative ad to open up the general election," Brown told reporters in Baltimore on Wednesday afternoon. "But in a way it doesn't surprise me because he doesn't have a record."
The political squabbling came as pundits predicted that this year's governor's race has the potential to be a competitive contest that attracts donors and attention from outside Maryland.
Democrats say Brown's bid to be Maryland's first African-American governor as well as his background as a first-generation American, a Harvard graduate and an Iraq War veteran is likely to attract interest from party activists outside the state.
"There's credibility to that," said Bob Fenity, executive director of the state's Democratic Party. He pointed to the primary night statement from Democratic National Committee chairwoman Debbie Wasserman Schultz that "Democrats are ready to unite behind the historic candidacy of Maryland Lieutenant Governor Anthony Brown."
The race could also attract GOP donors looking for big wins in Democratic states.
"People forgot that when Ehrlich won, the big word on his ads was 'moderate,' " said John T. Willis, a former Maryland secretary of state and author of a book on Maryland politics. "Hogan's challenge will attract national attention if he can make it seem competitive."
Both Brown and Hogan cruised to substantial primary victories Tuesday as they positioned themselves for the governor's job, which pays $165,000 a year to start.
Brown carried 20 of 24 jurisdictions among Democrats. And Hogan won every populous metropolitan county except Harford in the Republican race.
The Maryland Democratic Party, which remained silent through the $17.5 million, fiercely fought Democratic primary, jumped in the fray Wednesday to criticize Hogan. The state's Republican Party, in turn, broke its primary silence to rush to Hogan's aid.
Hogan's ad that sparked Wednesday's tiff was produced in sepia tones with a husky voice-over meant to mimic the popular Dos Equis "Most Interesting Man in the World" beer commercials. It was emailed to supporters and promoted online with a modest digital advertising buy, campaign spokesman Adam Dubitsky said.
The spot knocks Brown for tax increases, the state's bungled online health insurance exchange and Maryland's unemployment rate. It ends with a photo of Brown and running mate Ken Ulman flexing their biceps.
The last photo prompted state Democrats to decry the ad as "despicable."
The pose was part of a viral Internet campaign to commemorate a Howard County cancer patient named Zachary Lederer, whose similar double-armed biceps flex during his treatment became an Internet meme known as "Zaching." In using the photo, the Democratic Party accused Hogan of "politicizing a cancer victim's struggle."
Joe Cluster, executive director of the Maryland Republican Party, dismissed the criticism as hyperbole designed to distract from the ad's message.
"In no way does this ad politicize Zach Lederer's cancer struggles," Cluster said in a statement. "But it does highlight the future struggles of those Marylanders who need quality health care and will struggle to receive it because of Brown's failures as the head of the MD Health Benefit Exchange."
In several ways, the Brown-Hogan fight began before the primary ven ended.
More than a week before the election, Brown's campaign redeployed the political tracker who for months had been following Democratic rival Attorney General Douglas F. Gansler with a video camera.