Prime Minister Pedro Passos Coelho's "Portugal Ahead" coalition was on 39.16 per cent of the vote, according to results from more than three-quarters of constituencies, with the opposition Socialists of former Lisbon mayor Antonio Costa trailing by more than seven points yesterday.
A convincing win for the centre-right would be a huge turn up for the books for a government which pushed through four years of swingeing austerity, which sent unemployment and emigration soaring in western Europe's poorest country.
Passos Coelho campaigned on his record of having returned the country to fragile growth after one of the worst crises in its history, warning that the opposition Socialists could undo the progress.
His victory could signal a turning of the tide in Europe, with the austerity governments of eurozone Spain and Ireland about to face their electorates in the coming months.
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"We have had very tough times in past four years, with a lot of sacrifices. I am confident in the work I have done," Passos Coelho told journalists after voting in a Lisbon suburb.
The Socialists have vowed to ease the painful reforms they claim went further than its creditors demanded.
But many believe the Socialists lost the propaganda battle. "The right has succeeded in getting across the message that returning the Socialists would lead the country to bankruptcy," political scientist Antonio Costa Pinto told AFP.
Other analysts warned that if there was no clear victor Portugal risks a period of instability that could endanger its fragile recovery.
Costa, a fearsome negotiator, could block a minority centre-right government by joining forces with the Left Block and the Communists, who between them were on course for 16 percent support.
"Nothing will change anyway, austerity will continue," said Manuel Augusto, 75, who said he voted for the Socialists.