BUENOS AIRES, Brazil (AP) - Sao Paulo will face Atletico Nacional in the Copa Libertadores on Wednesday in one of the few matchups between former champions in this year's group stage.

Seven other matches in Latin America's most important club competition are also played this week, including a meeting between powerhouses River Plate of Argentina and America of Mexico.

Atletico Nacional, the 1989 champion from Colombia, will host Brazil's Sao Paulo boosted by a 1-0 league victory against rival Medellin on Saturday.

The club is seeking its first title since it beat Paraguay's Olimpia with a team led by goalkeeper Rene Higuita and coach Francisco Maturana.

Sao Paulo, a three-time champion, is looking to win the competition for the first time since 2005, when it beat local rival Atletico Paranaense.

The Brazilian club will have striker Adriano, who is on loan from Italy's Inter Milan. Coach Muricy Ramalho also will count on recently signed striker Eder Luis, a 22-year-old promising talent who joined from Brazil's Atletico Mineiro.

"It's not going to be an easy match," Ramalho said. "Their team gained confidence with the victory against their rival, but we have a team with experience in the Libertadores. It's going to be a very difficult group but we have to get through the first stage."

In Group 5, River Plate will host America on Wednesday trying to rebound from its opening loss to Peru's Universidad de San Martin.

"America is not doing well but we know it's going to be a tough opponent because it has great players," River Plate midfielder Augusto Fernandez said.

America will look for its second consecutive win after beating Chile's Universidad Catolica, which on Tuesday plays at San Martin.

Another Peruvian team leading its group, Cienciano, will travel to Brazil to face five-time Brazilian champion Flamengo on Wednesday at Maracana stadium.

Flamengo, the 1981 Copa Libertadores champion, is coming off a thrilling last-minute victory against Botafogo on Sunday to clinch Rio de Janeiro's Guanabara Cup.

In other matches Tuesday, Venezuela's Caracas hosts Bolivia's Real Potosi in Group 1 and Estudiantes de La Plata plays Lanus in an all-Argentine match in Group 2.

On Thursday, Venezuela's Maracaibo hosts Chile's Colo Colo in Group 3, while Colombia's Cucuta Deportivo hosts Bolivia's San Jose in Group 6.

The top two teams in each group will earn a spot in the next stage.