PITTSBURGH — This city’s last GOP mayor served during the Depression and Democrats outnumber Republicans 5-to-1, but business executive Mark DeSantis has emerged as a serious challenger to Democratic incumbent Luke Ravenstahl, in part because of the young mayor’s missteps.

DeSantis grew up in Sharpsville and graduated from then-Kennedy Christian High School in 1977.

A Republican who won the mayoral nomination as a write-in, DeSantis has government experience, is wooing black voters — despite their history of overwhelmingly rejecting GOP candidates — and is benefiting from a unique set of circumstances.

Ravenstahl is only 27 and was not elected to office. As City Council president, he was next in line to take over when then-Mayor Bob O’Connor died of brain cancer last September.

Ravenstahl landed feel-good spots on David Letterman’s “Late Show” and other national media outlets as the youngest mayor of a major U.S. city, but since then he’s stumbled — several times.

Most recently, Ravenstahl was criticized for using a special police SUV bought with federal Homeland Security funds to take his wife and friends to a Toby Keith concert. Ravenstahl said he did not know how the vehicle was purchased, and stopped using it when he found out.

“The fact that he went from ‘Golden Boy’ to Pinocchio, that is his biggest problem,” said Joseph Sabino Mistick, a law professor and longtime political insider who served as top aide to former Mayor Sophie Masloff in the late 1980s.

DeSantis, 48, runs a high-tech firm, is a former aide to the late U.S. Sen. John Heinz and was a science policy adviser to the first President Bush and later did similar work in the U.S. Department of Commerce.

The first mayoral debate Tuesday attracted a standing-room-only crowd, a sign the GOP has put forward a serious candidate and not just its traditional sacrificial lamb.

“The turnout and enthusiasm established this as a real race,” the Pittsburgh Post-Gazette editorialized, “where perhaps anything can happen.”

Unlike many Republicans before him, DeSantis is actually spending a significant amount on ads, including a daring TV spot that compares him to the city’s most famous ex-mayors, David L. Lawrence and Richard Caliguiri (both Democrats, by the way).

Still, no one is betting that DeSantis will necessarily take more than the 25 percent to 35 percent of the vote that Republican mayoral candidates typically manage in Pittsburgh.

“If all the stars aligned, there could be the making of an upset here, but it’s against the course of history and against odds,” Mistick said. “You just need a young mayor to keep making mistakes. The right one could be a deal breaker.”

Ravenstahl declined to be interviewed for this story, but he has said most of the criticism directed against him has been because of his age, not because of anything substantial.

DeSantis said it’s imperative to erase the city’s $1.1 billion debt and right-size a city government that, despite cuts in recent years, still appears to be shrinking more slowly than the city it serves. Since 1950, Pittsburgh has lost more than half its population, from 677,000 to about 312,000.

DeSantis’ platform has gotten mostly positive press as Ravenstahl’s peccadilloes have made his age more of an albatross than an advantage.

His response to the SUV flap also raised eyebrows.

Though saying he wouldn’t use the vehicle any more, he also said: “I’m still going to continue to be who I’m going to be, and go to concerts like I always have, and go to have a drink with my wife in bars.”

“That’s what 27-year-olds do and I shouldn’t be any different ....,” he said.

Pittsburgh Post-Gazette columnist Brian O’Neill said the response did not show great judgment and “the mayor’s answer invites the observation that one of the things a 27-year-old generally doesn’t do is run a major American city.”

In January, reports surfaced that then-Councilman Ravenstahl was briefly handcuffed while arguing with police outside a Pittsburgh Steelers game in October 2005. Ravenstahl said the dispute was a misunderstanding that he and the officer resolved at the time.

In March, Ravenstahl took a private jet to New York with Pittsburgh Penguins co-owner and Democratic Party heavyweight Ron Burkle just hours after the mayor helped negotiate a new state-subsidized hockey arena. Ravenstahl’s political organization later reimbursed Burkle.

A city ethics panel grilled him after the Penguins and a hospital network paid his $9,000 entry fee at a charity golf tournament in June. Ravenstahl said he did nothing improper and would continue to appear at charity events because it’s his job to promote the city.

Despite being handed such advantages, DeSantis won’t raise the $750,000 he targeted for his campaign because the biggest donors are hesitant to back a longshot, said Jim Roddey, the Republican powerbroker and former Allegheny County executive who is backing DeSantis’ campaign.

Roddey said the campaign will cut costs by doing without pollsters and should still be able to afford saturation ads just before the Nov. 6 election.

Meanwhile, critics say DeSantis can’t possibly deliver on promises to start paying off the city’s debt and cutting $193 million in spending over four years.

DeSantis brushes off such criticism. “When I talk about right-sizing government, the response is ’What are you going to cut?”’ DeSantis said. “What that presumes is that we are as efficient as we can possibly be.”

“We’re not even close to that,” he said.

Roddey said 30 Democratic committee members have defected to the DeSantis camp, while about 500 other Democrats are quietly supporting the campaign. Some of that’s occurring because other Democrats are maneuvering to challenge Ravenstahl in the May 2009 primary.

Some Democrats, like Darnell Greene, a black single mother, said they simply believe in DeSantis.

Greene was on active duty in the Army when she attended DeSantis’ lectures on how to help veterans start a business at Robert Morris University a few years ago. The two stayed in touch as Greene learned to run her convenience store in the city’s historically black Hill District.

“I’m actually a registered Democrat, but I definitely believe in Mark and what he’s about,” Greene said. “He says he’s a Republican, but he has a Democrat heart because he’s all about, like, people and the community and helping, too.”