Ukrainian President Petro Poroshenko has agreed to debate rival candidate Volodymyr Zelensky in a rare stadium event.
The incumbent has also agreed to take a drug and alcohol test on Friday.
A date has not yet been arranged for the televised face-off, which will take place in Kiev’s Olympiyskiy Stadium.
It comes days after Mr Zelensky, a comedian with no political experience, won the most votes in the first round of Ukraine’s presidential elections.
Mr Zelensky has since called for their debate to be moderated by Yulia Tymoshenko, Ukraine’s former prime minister who polled third in this week’s voting.
President Poroshenko responded by telling Mr Zelensky to “be a man” and “not hide anymore… I am waiting!”
Mr Poroshenko had earlier challenged Mr Zelensky to a debate before the first wave of voting.
The challenge was initially accepted but Mr Zelensky later backtracked on his pledge, a move which drew criticism on social media.
Then, on Wednesday, Mr Zelensky threw down the gauntlet in a slick social media video.
“You thought I’d run and hide…. no I’m not you in 2014,” he said, accepting the challenge and giving Mr Poroshenko 24 hours to reply.
The presidential hopeful also demanded the debate be held, in front of all interested broadcasters, at Olympiyskiy Stadium. The venue can hold up to 70,000 people.
On Thursday, Mr Poroshenko responded with his own, more sombre video, insisting that the stadium event not become a “show”.
“There’s no room for jokes here,” said Mr Poroshenko.
“Being a president and supreme commander is not a game… it means being responsible for the people, for the country.”
Both candidates have agreed to cover the costs of the event, as set out by Ukraine’s civil society watchdog Opora.
A bad miscalculation
By Jonah Fisher, Kiev Correspondent
Mr Zelensky’s unusual strategy of avoiding conventional political campaigning in favour of carefully calibrated social media videos has been working so far.
And then he challenged President Poroshenko to a debate – clearly thinking there was no way he would agree, and this “offer” would deflect attention from his own reluctance to participate.
He badly miscalculated. Mr Poroshenko has nothing to lose and would dearly love to lock horns with the inexperienced Mr Zelensky. Perhaps it’s the only way he might turn things around.
Mr Poroshenko called the comedian’s bluff. Mr Zelensky’s team started to panic. They declared the medical clinic unacceptable and suggested another one.
Then Mr Zelensky made an even stranger suggestion, that the defeated third-place candidate from the first round, Yulia Tymoshenko, should moderate the debate.
She and Mr Poroshenko have a longstanding rivalry, making the idea a complete non-starter as well as ridiculous.
This “stadium debate” affair may turn out to be simply a disastrous episode on Mr Zelensky’s path to the presidency.
But it is very strange that a man who has spent the campaign trying to convince people that he’s not just a comedian and can be serious, now appears to be trying to turn campaigning into a complete farce.