Incumbent Nestor Kirchner remains the strongest candidate ahead of the Argentine presidential elections in October, but he has recently shown signs of a weakness that he had managed to avoid since being elected in 2003.

"The right wing established a beachhead in the capital," the left-wing daily Pagina 12 said graphically.

On Sunday, voters preferred conservative businessman Mauricio Macri by 61 per cent to Kirchner's own education minister, Daniel Filmus, a candidate the president had actively campaigned for. Filmus took only 39 per cent in the run-off election, the nearly-complete official results showed.

Argentina also chose its first-ever female governor, Fabiana Rios, the candidate of centre-left coalition ARI, over Kirchner's favourite candidate. Rios will lead the southernmost Argentine province, Tierra del Fuego, after taking 52 per cent of the vote.

The results "are a direct message for the government's plans, although they cannot be mechanically transferred to the national dispute," analyst Eduardo Aulicino wrote in the Argentine daily Clarin.

Indeed, the local vote in Buenos Aires normally has little influence over national politics, but Sunday's elections are seen as an important political barometer and Macri's victory could take wind out of the sails of the government ahead of the presidential vote.

Macri made it clear Monday that his party is going to "work to achieve an alternative that balances the political system in October."

"People no longer hand blank checks. If anyone thinks he owns power is wrong," the Buenos Aires mayor-elect warned.

The pro-Kirchner camp has not yet said who will be its candidate in the October 28 election, although the president has repeatedly said "it will be a male penguin or a female penguin."

The gender reference to an animal characteristic of southern Argentina, from which left-wing Peronist Kirchner himself hails, has led analysts to say he could be a candidate, or that his wife, Senator Cristina Fernandez, could run. In either case, opinion polls point to a likely victory by the ruling party.

However, a handful of candidates have already made it clear that they will try to reverse the trend.

Former President Carlos Menem (1989-99), a right-wing Peronist, is set to try again to defeat the man who beat him for the presidency in 2003.

He will be joined by ruling-party dissident Roberto Lavagna, Kirchner's finance minister until late 2005, and ARI candidate Elisa Carrio. Along with them, the Argentine right wing will seek votes through Macri-ally Ricardo Lopez Murphy and the independent Jorge Sobisch.

However, none of these candidates appears currently in a position to be a serious threat to either member of the presidential couple, with the incumbent president scoring admittedly higher than his wife in opinion polls.

A recent study on a hypothetical election - carried out before the Buenos Aires runoff vote - gave Kirchner close to 57 per cent of the vote, relegating Lavagna to 9 per cent, Carrio to 7 per cent and Lopez Murphy to less than 3 per cent.

Alternatively, his wife, Senator Fernandez, would still come out ahead, but with only 47 per cent, to Lavagna's 12 per cent, Carrio's 10 per cent and Lopez Murphy's just over 3 per cent, the same poll said.

Sunday's triumph indicates that Macri is the current leader of the Argentine opposition, but he will not be in the race in October. Moreover, analysts agree that none of the incumbent government's rivals in the presidential election came out of the Buenos Aires vote significantly stronger.

However, Kirchner has undoubtedly been hit.

"The president will be forced to take precautions about his fundamental" path, analyst Joaquin Morales Sola said in the conservative daily La Nacion.