As the battle for the Democratic mayoral nomination moved into its final weekend, apparent front-runner Michael Nutter finally joined in the negativity, putting out a television commercial attacking Tom Knox.

The commercial, quoting from several newspaper editorials, called the millionaire businessman and former deputy mayor unsuited to run the city.

"Don't let Tom Knox's money buy the election," the ad concluded. "Philadelphia deserves better."

The ad was intended, at least in part, as a counter to two anti-Nutter mailings that the Knox campaign sent this week.

One called Nutter "part of Philadelphia's failed political system" and highlighted his links to "corrupt politicians." The other pointed out that Nutter spent three months after leaving City Council last year on the payroll of a consulting firm he helped get a contract with Council.

Knox, who was second in the most recent Keystone Poll, said he was not concerned about the latest Nutter ad.

"A lot will come down to integrity," Knox said. "Michael Nutter hasn't been showing a lot of good integrity in the last few days."

Meanwhile, Bob Brady, who is the city Democratic chairman as well as a mayoral candidate, was busy denying a story in yesterday's Philadelphia Daily News that he was freeing up some ward leaders to support Nutter in hope of guaranteeing Knox's defeat.

"I'm not releasing nobody," Brady said as he worked the lunchtime crowd at the Reading Terminal Market. "I'm running as hard as I can and doing it. I'm doing it as hard as I can."

Knox said he did not believe Brady's denial, saying he was convinced that party leaders were conspiring to defeat him.

"Bob Brady hasn't told the truth at all in this campaign, at least how it concerns me," Knox said. "Brady knows I'm going to put an end to pay-to-play politics. So he's mustering the troops because he doesn't want me in there."

Candidate Chaka Fattah, speaking to a noontime rally at JFK Plaza, also had a bone to pick with the Daily News. He was upset over an editorial cartoon by Signe Wilkinson showing two boys with bullet holes and quoting Fattah as saying, "But I will protect you from being stopped and frisked."

The congressman, who has criticized Nutter's calling for broader use of the stop-and-frisk tactic as a way to get illegal guns off the street, called the cartoon "insulting to our intelligence."

Fattah added: "Let's see what the voters say on election day about who's interested in protecting our young people from violence."

Later in the day, about two dozen Fattah supporters picketed the Inquirer and Daily News Building in protest.

Daily News editor Michael Days defended the cartoon, saying of Wilkinson: "The thing about Signe is that she doesn't shy away from controversy. She's biting, and always makes a declarative point in whatever topic she takes on, once she arrives at an opinion."

The fifth major candidate, Dwight Evans, held a news conference to underline his opposition to Brady's proposal to add an additional mayoral representative to the School Reform Commission, on which three of the five members now are appointed by the governor.

Evans, a key supporter of the state takeover of the Philadelphia schools in 2002, said that the system was working well as it is.

Today, Evans plans to kick off a 24-hour nonstop "Evans Express" campaign across the city. "I'm going to take it to the people," Evans said after shaking hands with commuters at 15th and Market Streets yesterday afternoon.

Nutter also received the endorsement of Local 835 of the International Union of Operating Engineers, which represents 1,975 skilled tradesmen at area universities and cultural institutions.

It was the first union endorsement that Nutter has received in the campaign.

Contact senior writer Larry Eichel at 215-854-2415 or leichel@phillynews.com.

Inquirer staff writer Robert Moran contributed to this article.