Meanwhile, Labour Party (LP) candidate, Mr. Fatai Akinbade, sent his running mate to stand in for him but the organisers disallowed him from participating, saying the rule did not allow for representation by proxy.
Organizers said they were shocked that Messrs Omisore and Akinbade failed to attend the debate.
"We wrote to them and up to 20 minutes to the beginning of the programme, they were still giving us the impression they would be attending", said Ezenwa Nwagwu, an official of the Partners for Electoral Reform, who moderated the debate on behalf of the IRI.
"We even started the debate 45 minutes late just because we were waiting for the PDP and LP candidates to show up".
However, Omisore has denied receiving a formal invitation letter from the organizers of the event.
His Director of Media and Strategy, Diran Odeyemi, said "It was only this morning that our candidate (Mr. Omisore) received a text message reminding him of the debate and that he was being expected at the OSBC studios".