Mr Unasa - head of the council's Pacific Peoples Advisory Panel - is chasing the Pasifika vote that helped Mr Brown beat John Banks in 2010.
He has been prompted to stand by "a lack of action for Pacific people" and Mr Brown's position on social justice issues, including the mayor's support for the SkyCity pokies-for-convention-centre deal.
John Minto, standing for the Mana Party, and Penny Bright have unashamedly left-wing agendas. Mr Minto is promising free public transport and paying council staff and council contractors the minimum wage of $18.40 an hour.
Ms Bright is promising to abolish the council-controlled organisations and publish the names and spending details of consultants and contractors used by the council.
John Palino is an unknown quantity when it comes to politics. The American who moved to New Zealand in 1996 is a restaurateur businessman who exudes a quiet confidence but has little in the way of policy at this stage.
What is known is that Mr Palino wants to build a new, modern city in Manukau and investigate Auckland's $59 billion integrated transport programme, which he says costs too much and delivers more congestion.
He also believes that the council bureaucracy is far too secretive, citing the decision of senior management to refuse councillor Sandra Coney access to a legal review of the Unitary Plan.
Mr Brown - with the advantage of incumbency, a mayoral budget of $4 million and a team of six spin doctors for self-promotion these past three years - is running with a campaign slogan that he knows "what matters to Aucklanders".
The centre-right has struggled to find a strong challenger to Mr Brown. At one point, National Cabinet minister Maurice Williamson weighed up his options but abandoned any bid for the mayoralty.
Some commentators believe the mayoral contest is a one-horse race. The danger of this perception is a low voter turnout, which normally favours the centre-right.
Add the promise of a well-funded and vigorous campaign by Mr Palino, the anti-Brown vote flooding his way and Mr Unasa, in particular, attracting Pasifika, Maori and ethnic votes, and Mr Brown could have a real fight on his hands.
And even if the mayor gets re-elected, he might find a different hue around the council table, one less friendly to the "inclusive" team he has come to rely upon.
The failure of the centre-right to unite around the Communities & Residents brand (with subsequent desertions from C&R this month) and the mixed bag of left-leaning councillors have worked in Mr Brown's favour in his first term.
It would take only a handful of new, right-leaning faces to tip the balance and make life difficult for the mayor. Pro-Brown councillors Michael Goudie and Des Morrison are stepping down in the respective conservative wards of Albany and Franklin. The centre-right is also targeting Cathy Casey (Albert-Eden-Roskill), Ann Hartley (North Shore) and Richard Northey (Maungakiekie-Tamaki).
Deputy Mayor Penny Hulse has taken umbrage at a call from Herald columnist Brian Rudman for candidates to embrace the labels of National, Labour and the like.
She says this would see a return to the bad old days of the former Auckland City Council with secret caucus meetings, one-term councils and three-year planning horizons.
She has coined the term "Auckland Party" for people who want to focus on the city and building for the future.
But even minus the C&R tag, there are enough issues uniting centre-right candidates - such as a low uniform charge that leads to bigger rates for high-value home owners and debt levels - to potentially scupper the "Auckland Party".
The looming election is already seeing changes made to the Unitary Plan, with word leaking out that height limits are being reduced in many town centres and "small-scale" apartment buildings banished from many residential areas.
Modifications to the draft Unitary Plan for formal notification in September is a political test for Mr Brown and his inner circle of Ms Hulse, Ms Hartley, Penny Webster and Mr Northey. Get it wrong and the Unitary Plan - the new planning rulebook that affects every Aucklander and every property - will become a big election issue.
Postal voting papers go out on September 20 and election day is Saturday, October 12.
The Auckland mayoral candidates on why you should vote for them:
Penny Bright
Len Brown
John Minto
John Palino
Uesifili Unasa
