Former Atlanta Mayor Shirley Franklin endorsed Mary Norwood's campaign, giving her campaign its most prominent supporter yet – and an important ally to reach African-American and Democratic voters - in the race for the city's top job.

The city councilwoman also received the endorsement of former Atlanta chief operating officer Peter Aman, a once-bitter rival who finished in fourth place in November’s election.

Both made Norwood's pledge to be a "fair and corruption-free" leader amid an ongoing federal probe into City Hall a theme of their endorsements, which were announced at a Monday press conference.

Norwood and Councilwoman Keisha Lance Bottoms are racing to lock up support from political power brokers ahead of next week’s runoff. Bottoms has the backing of Atlanta Mayor Kasim Reed and several leading Democratic figures, including gubernatorial candidate Stacey Evans.

Norwood, who would be Atlanta's first white mayor in 44 years, has countered with a growing number of her own endorsements. They include City Council President Ceasar Mitchell, who finished sixth in the November vote and endorsed Norwood last week.

The dual endorsements from Aman and Franklin give Norwood new, if unlikely, surrogates for the final stretch of the campaign.

Aman staked his campaign on targeting Norwood's north Atlanta base and constantly pummeled her at forums and debates, including labeling her a "corrupt career politician" in the final weeks of the race. But he also had little common ground with Bottoms and openly sparred with Reed.

The bigger surprise is Franklin, who offers Norwood a strong African-American ally in a city that's elected black mayors since 1973 and a prominent Democratic voice - Franklin co-chaired the national party's platform committee - as she's being pilloried as a "closet Republican."

(Norwood, who describes herself as an independent, said she voted for Barack Obama and Hillary Clinton and said her bipartisan attitude will help her work across the aisles.)

Franklin has long had a testy relationship with Reed, though she has also suggested she would steer clear of the contest to replace him. Her calculus seems to have changed as the political rhetoric ratcheted up and the Dec. 5 contest neared.

In mid-September, Franklin penned a quiet critique of Reed, without mentioning the incumbent, for what she said was the "complete and utter dismissal of the contributions" of his predecessors in the mayor's office.

And in November, she took aim at Reed's handling of the ongoing federal corruption probe that has engulfed City Hall – and cast a shadow over the race to succeed him. As she told our AJC colleague Jim Galloway:

"The adequate answer is 'I own that this problem happened on my watch,'" Franklin said.

Franklin's public support for Norwood represents the biggest break in an already fractured relationship with Reed, who was once her campaign manager.

Both have said little publicly about their strained relationship, but it seemed to grow chillier around the time Reed won the mayoral election in 2009. And the tensions escalated during the 2013 election when Franklin’s pick for an at-large Council seat, Andre Dickens, defeated a Reed-backed candidate.

Keep reading: Atlanta mayoral candidates piling up endorsements

More recent AJC coverage of the Atlanta mayoral race: