An open seat on the Miami-Dade Commission is so rare — and tantalizing — that perhaps it should be no surprise that this year’s race to replace outgoing Commissioner Joe Martinez has become such a no-holds-barred battle.

In their months-long campaign, political newcomer Manny Machado, former state Rep. Juan C. Zapata and their supporters have sniped over everything from stolen yard signs to their professional backgrounds to their personal dirty laundry.

The prize: representing Commission District 11, a stretch of unincorporated west Miami-Dade’s densely populated and largely Hispanic suburbs, including Lakes by the Meadow, the Hammocks and Country Walk.

With a chance to win a commission post without having to defeat a powerful incumbent, the stakes are high. Once elected, commissioners have been nearly impossible to unseat.

Two open seats came up for grabs last year, but that was unusual, with rushed special elections prompted by the recalls of Mayor Carlos Alvarez and Commissioner Natacha Seijas. The previous open-seat contest — two years ago, following the retirement of Commissioner Katy Sorenson — was fought tooth and nail.

Machado, a Miami-Dade police detective on leave to run for office, was born in Cuba — his father was a political prisoner — and moved to Miami when he was 5, during the Mariel boatlift. A married father of two, his wife is a volunteer reserve police officer for Virginia Gardens who operates M-Force Security Corp., a private security firm founded by her husband. He is no longer listed on the corporate records. Banks briefly sought to foreclose on the couple’s house a few years ago before the two sides reached a settlement.

Zapata, who is unmarried, was born in Peru to Colombian parents who moved their family to west Miami-Dade when he was 11. He is a partner in a local condo-management firm, Pazos Robaina & Zapata, and works as a business-development and public-affairs consultant, though he says his consulting clients are not in Miami-Dade.

On paper, Zapata, 45, would appear to hold the edge over Machado. More voters likely recognize his name, from his eight years representing portions of the district in the Florida House. Before that, he served on the local zoning community council. He has big-name endorsements from Mayor Carlos Gimenez and former Gov. Jeb Bush. And he has raked in more than five times as much in campaign contributions as Machado.

“The county’s a big, complex form of government,” Zapata said. “I’m the best qualified and the most experienced candidate to be able to give the residents of the area a voice.”

But the rookie Machado, 37, has hung in there. He has introduced himself to voters, in person and through mailed fliers. Before joining the police department in 2008, he worked for eight years as a state trooper, following a stint at UPS. As he walked door-to-door in West Kendall on a recent humid afternoon, he called the district a “jewel” and said he would work to keep it that way.

“I’ve always been active in the community, but always in uniform,” said Machado, who would have to resign from the police department if he were elected. “I’m running as a resident; I’m not running as a cop.”

The two candidates — both Republicans seeking the nonpartisan commission seat — have both campaigned against property tax-rate hikes and “wasteful” spending at County Hall. They both favor term limits for commissioners and are against moving the Urban Development Boundary along the county’s western and southern fringes.