"If they obtain more than 50 percent, it will be very difficult for Allawi," the expert said.
Bar the success in ensuring the landmark January 30 elections were held on time, the 59-year-old secular Shiite has little to vaunt since he was named by the old US-appointed governing council last June.
He made security a priority but the insurgency has worsened, power cuts still darken Iraqi cities and there are widespread corruption allegations.
"Allawi should be very proud that his government proved to be able to hold elections on time," said Allawi's political director Imad Shabib.
Others are less complimentary.
Haidar Mussawi, a spokesman for Allawi rival Ahmed Chalabi, said: "The security situation didn't get any better, perhaps even worse, nor did public services improve."
Allawi "has not been particularly successful as a politician, the interim government didn't really achieve anything," said Joost Hiltermann of the International Crisis Group, a think-tank.
Allawi, who survived an assassination attempt while an exile in London in 1978, returned after the fall of Saddam Hussein in 2003. Despite the critics, as prime minister he has earned a reputation as a tough leader.
"Iraqis feel a fairly strong resentment towards exiles who came in and grabbed power, but they crave stability and security, and he's talked the talk of security, though he hasn't walked the walk," said Hiltermann.
Shabib denied that Allawi is an opportunist and argued he had more legitimacy than many other exiles.
"Allawi was known among Iraqis inside during Saddam's regime. He was not the politician who became known to Iraqis only after the downfall of the previous regime."
The incumbent was close to the US Central Intelligence Agency in exile and is reportedly Washington's favourite for the premiership.
"People may prefer someone who has good relations with the US as the best way to reconstruct Iraq 
, " said Hiltermann.
Allawi's supporters also mention the need for continuity in tough times.
"Some say that we need continuity in order to build the security forces up, and institutional reform needs to go in the same direction to achieve a state," said Allawi's campaign manager, Adnan Janabi.
A recent survey by the Washington-based International Republican Institute said almost two-thirds of Iraqi respondents considered Allawi's time in office effective.
Used to decades of Saddam dictatorship, respondents said an ability to "show strength" was more important than ideology.
Allawi's administration has also been accused of corruption, although this did not feature largely in the election campaign.
"There's no doubt that the current government is highly corrupt and the US has closed its eyes to tremendous corruption," said Hiltermann.
"Allawi's government has inherited one of the most corrupt administrations in the world, but it's not itself. We're trying to build the institutions and eliminate the corruption," answered Janabi.
Yet even if Allawi does not stay in office, he could relish the opportunity of criticising opponents in a democratic arena.
"It's not always useful to be in government," said the campaign manager. "It can be good to be able to criticise, especially in periods when there are huge failures."