Juan Antonio Pizzi says Chile failed to take advantage of the absence of Lionel Messi in a 2-1 loss to Argentina at the Copa America Centenario on Monday.
The holders, who defeated the same opponents on penalties in the final to win the tournament on home soil last year, were undone by goals from Angel Di Maria and Ever Banega in Santa Clara.
Barcelona superstar Messi sat out the Group D match due to injury and Pizzi knows the defending champions missed an opportunity at Levi's Stadium.
"It's different [to play] against a team ... without Messi," he said.
"The danger he represents isn't [replicated] by another player.
"It was an advantage for us, but then the player who replaced him [Nicolas Gaitan] played a very good match with other strengths."
Pizzi is struggling to fill the void left by his Copa-winning predecessor Jorge Sampaoli, with the new coach having overseen four defeats in his first five matches in charge.
"I knew that taking the Chile job would be hard and difficult," he said.
"I'm not surprised, but still maintain belief.
"Mistakes came at bad times. We lost the ball in our own half [too often], allowed Di Maria to take advantage and from there every [mistake] was more costly, [because] the opposing team was organised better.
"It is unusual too commit so many errors with players that are very [usually] accurate in this area. Against this opponent, it is very difficult not to pay dearly [for that]."
The holders now face matches against Bolivia and Panama as they seek to carry the defence of their title into the knockout stages by advancing to the quarter-finals.
"The tournament is complicated," Pizzi said.
"There is a very big expectation on the part of all to progress. We know there will be very difficult games, and we should not be very clever to think that our team is superior to others ... we have to prove it."