Sebastian Kurz, the 31-year-old chief of the poll-topping centre-right People's Party (ÖVP) accused Chancellor Christian Kern of "poisoning" Austrian politics with "dirty campaigning methods".
Kern's Social Democrats (SPÖ) are facing an election fiasco after being linked to social media sites spreading anti-Semitic and xenophobic "fake news" about Kurz, who is also foreign minister.
Damning evidence emerged recently that the Facebook pages were masterminded by Kern's ex-advisor, controversial Israeli spin doctor Tal Silberstein.
Kern denies any knowledge of the affair but his party's image has been badly dented, with polls pointing to a third place behind the far-right Freedom Party (FPÖ) and the ÖVP in the October 15th ballot.
"You have poisoned the Austrian climate with the campaigning style you've imported into Europe," Kurz barked at Kern in Sunday's televised clash.
Kern hit back, pointing to recent media reports that the ÖVP had offered money to a member of Silberstein's team to share information about their activities.
"Don't play the sacrificial lamb, I've worked with you for 15 months," snapped the 51-year-old who swapped his job as railway chief to become chancellor in May 2016.
The smear scandal -- which saw both parties sue each other last week -- overshadowed most of the 60-minute debate, described by media as a "hate duel".
The sworn rivals also fought over key issues like tax reforms and refugees.
As foreign minister, Kurz was instrumental in shutting down the so called western Balkan migrant trail and is now also pushing for the closure of the dangerous Mediterranean route.
His hardline stance helped catapult the ÖVP into pole position after he took over the reins in May and pulled the plug on the decade-long unhappy coalition with the Social Democrats.
Kern, meanwhile, has been unable to heal big rifts tearing his party apart.
Disagreements persist over how to manage a record influx of asylum-seekers and, more importantly, whether to break a major taboo and consider sharing power with the far-right FPÖ -- which looks set to be part of the next coalition government.