With his Syriza party still reeling from an insider anti-austerity revolt that toppled his government in August, Tsipras could be upstaged by his conservative rivals in the New Democracy party, who promise a return to stability after months of economic upheaval.
Both conservative leader Vangelis Meimarakis and Tsipras have pledged to stick to the tough reforms demanded by cash-strapped Greece's international creditors in July, meaning that economic policy going forwards is largely set in stone for whoever wins the September 20 vote.
"It's the first time I've felt so powerlesss to make an estimate. The entire political scene is like a boiling cauldron," Paschos Mandravelis, a columnist for liberal daily Kathimerini, told AFP.
Tsipras has a final chance to steal a march later Friday with a closing rally in central Athens, where he will be joined by Pablo Iglesias, leader of Spain's anti-establishment Podemos party.
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The leftists are accused of brinkmanship in negotiations with EU creditors that prompted the European Central Bank to hold back support for Greek banks, forcing Athens to impose capital controls that are still keenly felt in the economy.
Had he refused to sign, he argues, Greece would likely have been ejected from the eurozone.
- 'Tug the rope' on debt -
Today, he told Antenna TV that he would "tug the rope" in order to secure relief on Greece's huge national debt from EU creditors in the coming months.
"The timing is probably more positive for Greek claims, Europe is tired of having the Greek crisis constantly returning to the agenda," Tsipras said in another interview with Ta Nea daily.
Tsipras called the vote to try to win an outright majority in parliament after the split by anti-euro hardliners in his Syriza party.