Brazil President Dilma Rousseff would win a second-round runoff against either opponent and has 38 percent of voter support ahead of her October re-election bid, a new poll by the IBOPE polling institute showed on Tuesday.

    Her main challenger, Aecio Neves, has the backing of 22 percent of potential voters while Eduardo Campos has 8 percent, according to the survey broadcast on TV Globo.

The changes in voter intention for all candidates are within the poll's margin of error from June, when Rousseff had 39 percent of support, Neves had 21 percent and Campos 10 percent, suggesting Rousseff's support is not eroding as other recent polls have suggested.

The approval rating of her government remained at 31 percent, unchanged from a month ago when Brazil was starting to host the month-long soccer World Cup. Her personal approval rating was also unchanged at 44 percent.

The tournament was considered a surprising logistical success but moral in the soccer-loving nation was hurt by the national team's stunning 7-1 loss to Germany.

In a second-round runoff vote, Rousseff would defeat Neves of the centrist PSDB party with 41 percent of the vote compared with his 33 percent, IBOPE found. She would also win with 41 percent against Campos, a former state governor and leader of the Brazilian Socialist Party, who would get 29 percent.

Other polls released by Datafolha and the Sensus polling institute on Friday and Saturday showed the election headed to a runoff, with Rousseff and Neves tied in a second round.

Until recently Rousseff appeared to be cruising toward re-election, but she now finds herself in an unpredictable race almost certain to go to a runoff vote as an already sluggish economy takes a turn for the worse.

Her popularity has been declining this year due to concerns about high inflation as well as economic growth. Discontent has been on the rise since protesters took to the streets a year ago, and 70 percent of those interviewed in July desired change.

IBOPE's new survey was slightly different from a month ago because it asked respondents to choose between all official candidates to appear on the ballot, not just the favorites.

The poll surveyed 2,002 people from July 18-21 and has a margin of error of plus or minus 2 percentage points.