Defending Copa Libertadores champion Flamengo of Brazil were trashed 5-0 at Ecuador's Independiente del Valle on Thursday in their first match in the tournament in six months.
Del Valle, the reigning champion of the Copa Sudamericana, opened the scoring in the 40th minute with Moises Caicedo.
Their four other goals came in the second half with Angelo Preciado (49), Gabriel Torres (59), Jhon Sanchez (81) and Beder Caicedo in the second minute of stoppage time.
Catalan coach Domenec Torrent, a former assistant of Pep Guardiola in Barcelona and most recently the manager of NYCFC, admitted that the altitude 9,350 feet up in Quito affected his players.
"I know that this is the worst Flamengo result [ever at Copa Libertadores]," he said. "But this match is now over and we have to try to win the next match. As I said before, this is a mini league, not a 2-match [playoff]. If it was, it would be a complete disaster.
"This is a disaster too but, as a little league, it's three points. We will try to recover ourselves to the next match," he said. "Everybody knows that playing here [in the altitude in Ecuador] is not easy. It's not an excuse for the players and for me but that's what happens when you play here. We could have played better. We will have to play better!
"We played with more organization in the first half and that's why they scored only one goal and we had some chances counter attacking," he said. "But, in the second half, we decided to attack and put pressure at their defensive line.
"We knew, from the previous match against them that we watched, that they play together for a long time -- and very well. They play well when they have spaces.
"Without spaces, they have more difficulties. We decided that strategy for the second half. This [group stage] is a small league, not a 2-game [playoff]. It's just three points. It's a very painful loss We have to apologize to the fans."
Del Valle coach Miguel Angel Ramirez said he was surprised but added that his players worked together for the win.
"We didn't expect such a high score against the current champions of the America, the second team in the world, due to the skills that they have," he said. "We did know that we were working to dominate, we wanted to control spaces. That, if we were playing well, they wouldn't create plays.
"The Flamengo from Recopa had very different offensive behavior regarding the positioning of players. Because of that...it could be that... it was a little bit easier to defend nowadays," he said. "And being what they are, having the skills that they have. Individually, they can control you, win spaces, they are very good. As individuals.
"We, as a team, I personally have no doubts that we are way better."
Flamengo, who have struggled since the departure of coach Jorge Jesus to Benfica in July, also saw defender Gustavo Henrique be sent off in the closing seconds of the match in Quito.
The South American tournament restarted this week after a halt that began on March 12, at a time when nearly all cases of COVID-19 came from other continents.
Now Brazil, Peru, Colombia and Argentina are among the top 10 countries in the world in terms of confirmed cases of the disease.
Del Valle lead group A after three matches with nine points. Flamengo are second with six.
Torrent is already under pressure from supporters as Flamengo have lost four of his 11 matches in charge.
In less than a year, Jesus took the Rio de Janeiro giant to five titles, including their first South American crown in 38 years. The team also lost four matches under his orders, including the Club World Cup final against Liverpool in December, but won staggering 43 out of 57.
Asked whether he feels that he is under any threat to lose his job, Torrent laughed and said: "I don't know. I have something very clear: I will work hard, I have always worked hard.
"It's always the same for head coaches. When you win, everybody is happy. When you lose -- and this is a very painful loss of 5-0... What will happen? I don't know. I don't decide anything. I am focused on working and so are the players. But now, I don;t think it's time to talk about this. If you want to talk about this, you have to reach other people, not me."
Also on Thursday two Argentinian giants overcame their own expectations after a long period of inactivity. 2019 runner up River Plate drew 2-2 at Sao Paulo, with their players scoring all the goals of the match.
Enzo Perez opened the scoring with an own goal in the 10th minute, but River got level eight minutes later with Rafael Santos Borre from close range. The Argentinians scored the second with a strike from Julian Alvares in the 80th minute, but Sao Paulo put the final number in the scoreboard with another River own goal by Fabrizio Angileri three minutes later.
While River started training only weeks ago, Sao Paulo have played competitive matches since July. The result at the Morumbi kept the Argentinians and the Brazilians tied after three matches with four points in group D, which is led by Ecuador's Liga de Quito.
Boca beat Paraguay's Libertad 2-0 in Asuncion after a week in which 22 of their players had tested positive for COVID-19.
Many were allowed to play anyway because football authorities considered they had already recovered.
Eduardo Salvio scored a brace for the Argentinians, with goals in the 6th and in the 84th minute. Boca now lead group H with seven points, one ahead of second place Libertad.