The three-hour event debate between AKP candidate Binali Yildirim and the opposition's Ekrem Imamoglu was one of the first of its kind in Turkey in nearly two decades.
The two contenders for the mayorship of Istanbul took part in a rare TV debate this weekend.
The vote is being rerun after claims of electoral irregularities in the original ballot and is seen as a test of Turkish democracy and President Recep Tayyip Erdogan's AK party.
The opposition Republican People's Party candidate, Ekrem Imamoglu, won the first vote by a mere 14 thousand votes.
He's being challenged by former Prime Minister, Binali Yildirim from the ruling Justice and Development Party.
For Erdogan, his candidate's loss was was one of his biggest election setbacks since the AKP first came to power in 2002.
His party also lost control of the capital Ankara.
The decision last month to re-run the election raised new questions over Turkey's institutional independence.
The High Election Board scheduled the re-run on June 23 after a series of AKP complaints that the initial vote was marred by irregularities.
"Strange thing happened when your votes were counted," Yildirim said, describing the March contest.
"Votes were stolen," he said, without naming any culprit.
"Who stole votes for God's sake?" responded Imamoglu, saying the election board had made no such allegation in its decision to annul the vote.
"We are conducting a struggle for democracy. It is a struggle for Istanbul, for normalisation, for a clean administration free of arrogance."
The three-hour event, which ranged from Turkey's economic troubles and the large numbers of migrants in Istanbul to the shortage of green spaces in the city of 15 million, was broadcast on all major channels. Large screens were also set up in the streets.
WATCH: Nial O'Reilly's report on Sunday's debate: