The country is seeking to emerge fully from the dark days of General Alfredo Stroessner's dictatorship, which it endured from 1954 to 1989. Even if the Colorado candidate, Juan Carlos Wasmosy, triumphs, Paraguay will at least have its first civilian head of state in living memory.
But an opposition victory would confirm a new era: the outgoing President, General Andres Rodriguez, was elected by popular vote in gratitude for his overthrow of Gen Stroessner in a palace coup, but his has always been considered an interim administration, correctly-behaved but tainted by links to the former regime.
The Colorados talk confidently of victory in the free and fair vote. Recent polls indicated Mr Wasmosy at best running neck-and-neck with the opposition candidates, but the power of the Colorado party machine should not be underestimated. Since the 1989 coup, membership has fallen, as it stopped being a requisite for advancement, but it is still around 750,000 out of an electorate of 1,7 million - enough to secure victory if sufficient pressure is placed on dissenters to return to the fold.
Confronting Mr Wasmosy is the veteran campaigner against the dictatorship, Domingo Laino of the traditional opposition Authentic Radical Liberal Party. An independent centrist candidate, Guillermo Caballero Vargas, backed by the newly founded National Encounter alliance, appears to be losing ground and he may yet be remembered as the candidate who split the opposition vote. None of the parties seems likely to secure a majority in Congress.
Opposition voters - a majority of Paraguayans - are excited at the prospect of removing the Colorados from office. This is tempered by anxiety that the old guard will somehow conspire to cling to power.
Few observers believe a coup is likely. Were this to happen, people say division within the armed forces and massive popular rejection would ensure it would collapse from within. Questioned on Wednesday, Mr Wasmosy said the military had changed and would definitely accept an opposition victory.
But years of dictatorship have made the electorate wary. When the army strongman, General Lino Oviedo, declared in late April that the armed forces could continue to govern in partnership with the Colorados 'come what may', many Colorado and opposition supporters felt a chill down their spine.
Mr Rodriguez has made no move to dismiss Gen Oviedo, commander of the powerful 1st Army Corps which was his own vehicle to oust Gen Stroessner. What the old guard fears most is the loss of privileges secured under Stroessner, which allowed most of the generals and senior government officials to make fortunes in this poor country. Generalised corruption flourished, involving control of smuggling, 'recycling' of official funds such as road tolls and inflating the value of contracts in order to skim off the surplus.
There is restlessness over judicial investigations, which have already placed several human rights offenders behind bars and led to charges against some officers - including the former head of the army - for corruption. Analysis of the secret police files unearthed last December is certain to lead to more charges being laid against those involved in the disappearance of political prisoners.Reuse content