THE MAYOR'S RACE has officially shifted into oh-no-you-didn't mode now that the primary election is just three weeks away.

For proof, look no further than the debate hosted yesterday morning by WHYY that saw three of the Democratic mayoral candidates take metaphoric golf clubs to former City Councilman Jim Kenney, who, according to a pair of recent polls, is now leading the race.

Toward the end of the program, Kenney was asked how he'd respond to concerns that electricians union leader John Dougherty - a key supporter - would wield serious influence over a potential Kenney administration.

Kenney said he appreciated Dougherty's support, and noted the two grew up together. But Dougherty wouldn't have "any undo influence," Kenney said. "I know how to say no."

Kenney said he had a diverse collection of supporters, and noted that state Sen. Anthony Hardy Williams was also endorsed by labor unions.

Williams, the race's longtime presumed front-runner, unexpectedly pounced.

He said Kenney indicated months ago that he couldn't afford to run for mayor, only to jump into the race after Dougherty put his significant financial muscle behind him.

Former Common Pleas Judge Nelson Diaz chimed in, accusing Kenney of being disingenuous about his connection to Dougherty.

Even former state Sen. Milton Street took jabs at Kenney, accusing of him of being an "obstructionist" when Street's brother, John Street, pushed his Safe Streets anti-violence plan as mayor.

Tough crowd, man, tough crowd.

Kenney had to wait until the closing remarks to respond. He said he decided to run for mayor so that he could help working families - and then took a shot at the "three hedge-fund billionaires" who support Williams.

(If you're somehow just tuning in, Williams' campaign is backed by American Cities, a SuperPAC run by a trio of wealthy Main Liners.)

Beyond the sharp elbows, the candidates all touched on well-worn talking points.

Former District Attorney Lynne Abraham ran through her "tough cookie" credentials, while also selling herself to younger voters by calling for upgrades to the city's technological infrastructure, and for Philadelphia to replicate New York City's elevated High Line park.

Street drew laughs when his phone rang during a question about technology.

"I thought I turned this off," he said. "Shows you what I know about technology."

Former Philadelphia Gas Works spokesman Doug Oliver addressed concerns that he lacks the necessary experience to be mayor by noting that none of the other candidates had run the city before, either.

Kenney, Williams and Diaz all riffed on various fights they've waged: Kenney, for LGBT rights and the decriminalization of possessing small amounts of marijuana; Williams, for education funding in Harrisburg; and Diaz, for civil rights and equal rights for women.

On Twitter: @dgambacorta