The expected no-show by actor Volodymyr Zelensky prompted Poroshenko to stage a solo appearance on Sunday at Kiev Olympic Stadium as several thousand supporters flooded a nearby square.
Two podiums were set up at the stadium’s makeshift press centre and a moderator set down rules in front of journalists.
Outside the sports arena, Poroshenko’s supporters chanted his name and urged Zelensky to show up.
With one week to go before the vote, Poroshenko, 53, accused his rival, a 41-year-old political novice, of avoiding hard-hitting questions.
He also said he would respect the “choice of the Ukrainian people” if Zelensky were elected president on April 21 but added he was worried for the country’s future.
“I do not like that a presidential campaign in Ukraine looks like a silent movie,” Poroshenko said, standing next to Zelensky’s empty podium.
“I must say: Ukraine’s fate is in danger,” he said at the end of his hour-long appearance.
Zelensky had called for a debate to be held at the venue two days before the runoff vote. Poroshenko said that the date would conflict with the obligation to hold a debate at the studios of the national television channel.
Dmytro Razumkov, Zelensky’s campaign team member, was quoted by Ukraine’s Pravda publication that Sunday’s incident was a public relations stunt by Poroshenko.
“It’s well known that we are expecting [Poroshenko] on the Olympic Stadium for the debates on April 19 at 7pm. The fact that Zelensky would not be there today was known in advance. For some reason, Poroshenko wanted to go there today and he accomplished what he wanted,” he said.
Poroshenko has been scrambling to recover lost ground in a bruising campaign as polls show Zelensky easily defeating the incumbent for the leadership of a country locked in a war with Moscow-backed separatists.
Zelensky, whose political experience is limited to playing a president on TV, has shunned traditional rallies, instead, performing satirical shows.
But he capitalised on frustration over mainstream politics, war with Kremlin-backed rebels, poverty and corruption to defeat Poroshenko in the first round of voting on March 31.
Support for the comedian among voters has doubled to 61 percent since then, with Poroshenko at 24 percent, according to the Rating pollster.
Poroshenko has touted himself as the only candidate able to stand up to Russian President Vladimir Putin and repeatedly urged the comic to hold several rounds of policy debates.
At the sports arena, Poroshenko repeated that debates were not scary. “Do not be afraid,” he taunted his rival.
“I have come, you are not here,” Poroshenko added, citing a line from a humorous folk song.