The race for the city's top job heated up when Foster made an eleventh hour bid with financial backing from film-maker Sir Peter Jackson.
The pair have been vocal critics of a proposed development at Shelly Bay, with Jackson entering a well-aired keyboard battle with the city council and developers.
Foster has been a city councillor for 27 years and has made two unsuccessful mayoral bids during that time.
He said the city was losing its way.
"I've never had so many people say they want a change, and ask me to run for Mayor. They are very unhappy about what's been done, about what has not been done, and about the way things have been done."
Foster is running as an independent whereas Lester is running on the Labour ticket.
Lester announced his bid for another term early in the game.
When the incumbent was voted in as mayor in 2016 he was so nervous about living up to expectations his campaign manager gave him a shot of Jagermeister, which he swiftly "necked".
Now, almost three years on from that night he said he felt confident about where the city is and what he has delivered during his first term.
This final live debate follows two lively mayoral debates in Auckland and Christchurch hosted earlier this month by du Plessis-Allan (Auckland) and Newstalk ZB Christchurch host Chris Lynch, ahead of local body elections on 12 October.
"With transport and infrastructure two of the major issues in our capital city, and both candidates' views on these differing, tonight's clash promises to be as energetic as the others", du Plessis-Allan said.
