If the results hold, Sadr, a strident critic of the United States who commands a militia that fought USA troops during the occupation of Iraq, could be in pole position to determine Iraq's next leader.
Each Sadr and the chief of the ex-combatant Conquest Alliance, Hadi al-Ameri, have pitched themselves as trying to sweep clear Iraqi politics.
In a televised address Monday afternoon, Abadi hailed the "winning lists" and called on all sides to "respect the results", after calls for a recount in the multi-ethnic province of Kirkuk. Sadr's nationalist alliance, Saeroun, as the front-runner, and Sadr himself as expected kingmaker.
Several senior political figures had previously told AFP that preliminary results put Abadi in the lead, on course to scoop 60 of the 329 parliament seats up for grabs.
Abadi - who came to power as ISIS swept across Iraq in 2014 - has been a consensus figure who balanced off the U.S. and Iran.
That means it is entirely possible that Sadr could pick the next Iraqi government by deciding which political party to form a coalition with.
BAGHDAD The surprisingly strong showing of a ticket backed by maverick cleric Moqtada al-Sadr in Iraqi elections over the weekend will force US officials to recalculate how best to proceed in the region at an especially sensitive moment.
The vote got here with tensions surging between the US and Iran after Washington's withdrawal from the 2015 nuclear deal, sparking fears of a destabilising energy wrestle over Iraq.
Initial results indicate that the Sairoon coalition won between 54 and 56 out of 328 parliamentary seats, followed by the Al-Fatih bloc (between 40 and 44 seats) and the Al-Nasr bloc (between 40 and 42 seats), according to a source at Iraq's official electoral commission.
After the announcement that the Marching Towards Reform was ahead in Baghdad, supporters took the streets in the capital to celebrate a win.
Crowds of primarily younger folks waved flags and photos of the populist nationalist cleric Sadr whereas fireworks fired off into the evening sky.
More than 24 million Iraqis were eligible to vote in the elections, the fourth national election since the fall of Saddam Hussein and his dictatorial regime in 2003.
Zeid al-Zamili, 33, described the vote as "a victory over the corrupt" and a "new chapter for the Iraqi folks". "We support a fair and transparent process", he said. His supporters celebrated in Baghdad.
"Today we finally have hope", said local Ghassan Matar.
Over two million folks stay internally displaced throughout the nation and IS - whereas weakened - nonetheless has the aptitude to launch lethal assaults.