Political polls in Chile indicated that either candidate would trounce the right-wing Alliance nominee Joaquín Lavín in a two-person race.

The political atmosphere changed, however, when another Alianza candidate came to the scene: businessman Sebastián Piñera from the center-right National Renewal.

In previous elections the candidates presented independently by the pact's parties were consistently in third place, behind the two major coalitions, and holding poll numbers in the single-digit level.

Two candidates withdrew before the survey and gave their support to Hirsch: Tomás Moulian (Communist) and Manuel Jacques (Christian Left).

Considered for a long time prior to the 2005 election as the Alliance's unique candidate, as the contest drew nearer, however, his public persona began to lose credibility, perhaps due to a mediocre mayorship of the Santiago municipality the previous years,[citation needed] and his candidacy began to lose steam, to the point that it was called into question.

Huilcamán appealed using the argument that in the past parliamentary election there was a law created specifically to help the candidates of the Christian Democracy Party re-register their candidacies.

Among the elected, 20 seats are held by the CPD (eleven Christian Democrats, five Socialists, three PPD and one PRSD) and 18 by the APC (six independents, six UDI and six RN).

Of the Senate seats being contested, eleven were held by the CPD (ten Christian Democrats and one Socialist) and nine by the APC (four independents, three UDI and two RN).

The first debate, titled Foro Presidencial: Chile 2005, organized by the Latin American station CNN en Español and the local Canal 13, took place on 19 October, at 10 p.m., at Espacio Riesco in Santiago.

Opinion polls released after Sebastián Piñera's entrance and Soledad Alvear's withdrawal showed Michelle Bachelet leading the right-wing candidates (Piñera and Joaquín Lavín) by a wide margin, but below the 50% plus 1 vote needed to win the election, a situation that would lead to a runoff in which, according to the same polls, she would comfortably defeat any of the two right-wing candidates.

Some analysts commented that in some of these polls Bachelet would indeed have obtained an absolute majority in the first round, if blanks were discarded and undecided votes were evenly distributed among candidates.

The polls released showed on average that Bachelet maintained an advantage over Piñera above 5%, but with a large number of voters (18%) still undecided or that would not declare a preference.

If this last percentage was removed from the vote, then Bachelet, the polls showed, would have won the presidency by a margin above 7%, which was accurate with the final results of the election.

The first government announcement regarding election results came at 6:30 p.m. local time (21:30 GMT), and included information from around 12% of polling stations counted.

Subsequent preliminary results were announced during the day by the Interior Ministry undersecretary and published on a special Internet site.

Later in the day, JPM candidate Tomás Hirsch said he would nullify his vote in the upcoming runoff; an opinion which was objected by the pact's Communist wing, which said they would support Bachelet if five proposals delivered to her were accepted and incorporated into the candidate's government program; these proposals dealt with changing the electoral system and granting workers more rights.

Sebastián Piñera conceded defeat immediately following a government announcement made on election day that included results from 97.52% of ballot boxes counted.