A leading member of Georgia's main opposition party - former President Mikheil Saakashvili's United National Movement (UNM) - appears to have been the target of a terrorist attack on Tuesday evening after his vehicle was hit by what most experts believe was a massive auto bomb that left five people injured.
The rally by the United National Movement drew more than 25,000 amid growing public discontent about economic difficulties and disillusionment with the government.
The pro-Western Free Democrats and the pro-Russian Alliance of Patriots may be among those who clear the 5 percent threshold needed to get into the 150-seat parliament, analysts say.
Each of the two main parties carries substantial baggage.
Saakashvili is vowing a triumphant return if his United National Movement supporters in Georgia win power.
The UNM has accused the Georgian Dream government of orchestrating a political witch-hunt after members of Saakashvili's team were probed and some jailed since the Georgian Dream party defeated UNM in parliamentary and presidential elections in 2012 and 2013.
A hard-fought, often grubby and latterly violent campaign period has heightened long-held animosity between the ruling Georgian Dream party and the United National Movement (UNM) of Mr Saakashvili's allies.
Although Ivanishvili does not now hold office, he is believed to still wield enormous influence.
Saakashvili addressed the rally in a video call from Ukraine, where he works as the governor of the Odessa region on the Black Sea after receiving Ukrainian citizenship.
According to police reports, UNM lawmaker Givi Targamadze was seated in the front passenger seat of his auto when the blast occurred.
In other pre-election violence, two men were shot and wounded on Sunday at an open-air speech given by independent candidate and former defense minister Irakly Okruashvili in the town of Gori.
"We have noticed in the past couple days - that event in Gori and a vehicle bomb - that tension is increasing, but we hope that all the parties will do their best in order not to have a tense election day", Guglielmo Pucci, head of the Organization for Security and Co-operation in Europe contingent monitoring the election, said.
Saturday's knife-edge parliamentary election will see the UNM and the ruling Georgian Dream party clash in a bitter power struggle.
Although its 3.5 million eligible voters are faced with almost three dozen parties and blocs vying to fill the unicameral parliament's 150 seats through a mix of party lists and single-seat constituencies, the elections are effectively a showdown between Georgian Dream and Saakashvili's United National Movement (ENM).