RIO DE JANEIRO, April 11 (Reuters) - Sao Paulo and River Plate, two of the favourites to win this year's Libertadores Cup, face difficult matches at high altitude this week when they attempt to recover from shock defeats.
Both need good results to avoid the danger of first-round elimination in South America's equivalent of the Champions League.
Champions Sao Paulo travel to the Peruvian Andes to face Cienciano in the historic city of Cusco at 3,000 metres above sea level on Wednesday.
The Brazilians are second in Group One with six points from four games and cannot afford any more slip-ups after last week's shock 2-1 loss to Mexico's Guadalajara.
The defeat ended a 30-match unbeaten home record in the competition stretching back to 1987.
Cienciano, bottom with three points, will be playing their first game under former Peru coach Julio Cesar Uribe, who was known as the Black Diamond during his playing days.
A win would keep the Red Fury in with an outside chance of qualifying.
Venezuela's Caracas FC, who are third with four points, also have a chance to increase the pressure on Sao Paulo when they host Guadalajara the same evening.
Guadalajara have already qualified and will be without the six players chosen for Mexico's provisional 26-man World Cup squad.
The top two teams from each group progress to the next round.
River Plate, meanwhile, will be playing 200 metres lower than Sao Paulo when they visit Quito to take on Ecuadorean army club El Nacional in Group Eight.
Like Sao Paulo, River - champions in 1986 and 1996 - are second in their group and have no more margin for error after losing to Brazilian second division side Paulista last week.
River, led by former Argentina captain and coach Daniel Passarella, have six points, one ahead of Paulista, with two matches each to play.
Paulista, who qualified by winning last year's Copa Brasil knockout tournament, are away to group leaders Libertad of Paraguay the same evening.
Two groups will be settled on Thursday night including Group Two where Santa Fe (Colombia), Estudiantes (Argentina), Sporting Cristal (Peru) and Bolivar (Bolivia) are all level on seven points on five games.
Santa Fe face Cristal in Bogota and Estudiantes, champions three times in a row in the late 1960s with a notorious team featuring Carlos Bilardo, host Bolivar in Buenos Aires.
Three teams will be scrapping for two places in Group Seven where 1999 champions Palmeiras of Brazil, who have nine points from five games, have already qualified.
Colombia's Atletico Nacional, who are second with seven points, are away to Rosario Central of Argentina, who are third with five.
Paraguayan champions Cerro Porteno, who also have five points, travel to Sao Paulo to face Palmeiras.
Chilean champions Universidad Catolica and Brazilian champions Corinthians, who lead Group 4 with 10 points from five games, could both qualify without playing on Tuesday if Mexico's UANL lose at Deportivo Cali.
UANL have six points from four games while the Colombians have yet to pick up a point.