Hamilton City Council, as with previous events in the city, including the 2009 David Tua fight, refused to comment on whether it had tapped into its $450,000 partnership fund - aimed at bringing events to the city's facilities - to lure the event, citing "commercial sensitivity".
However, there was no funding from the council's $1 million events sponsorship fund, which has to be approved by a select group of councillors.
The Herald understands the council has been reassured there is no financial risk and the deposit for the event was received before Williams' original opponent, Richard Tutaki, was axed after a raft of criminal allegations were revealed.
Williams, 26, will now fight American Clarence Tillman III for the New Zealand Professional Boxing Association title.
Premium table tickets for the All Black's fourth fight were more expensive than the $4995 tables for the David Tua vs Shane Cameron fight at Mystery Creek Events Centre in October 2009. But the cheapest tickets are going for $43 compared with $50 for the 2009 fight, which was watched by about 11,000 people.
Hamilton boxing trainer and previous New Zealand amateur titleholder Dion McNabney said he had decided against attending because he was disappointed by the undercard fights so had opted to watch it on TV. He said Williams and Tillman were the best pairing and would put on a good fight. "It's a really big step up for Sonny Bill."