Chile caused Spain problems before and after Marco Estrada saw red
Chile coach Marcelo Bielsa felt Marco Estrada's sending off was the turning point in his side's 2-1 loss to Spain.
Estrada was dismissed after being adjudged to have fouled Fernando Torres in the build-up to Spain's second goal.
Bielsa, whose team joined Spain in the last 16 of the World Cup, said: "The game was even until the sending off.
"The first 40 minutes were balanced in possession, in control and in terms of goal chances. Evidently, afterwards it was a different match."
Chile caused Spain problems before going behind when keeper Claudio Bravo raced from his line and smashed the ball straight to David Villa, who netted from 45 yards.
When Andres Iniesta doubled the European side's lead and Estrada was dismissed for a second bookable offence, Chile were left facing an uphill task.
But they responded with a second-half goal from Rodrigo Millar, and went through to the knockout phase despite their defeat because Switzerland could only manage a 0-0 draw with Honduras.
Bielsa has steered Chile into the last 16 of the World Cup
Bielsa also bemoaned the defensive errors that contributed to Spain's goals.
"Spain's goals weren't just down to their own merit," he admitted.
"Maybe we could force Spain to play below their level, but that means not making big mistakes - and we weren't able to have that.
"We never thought we were better than Spain, though we could compete with them on an equal footing. But from the 40th minute, the match changed its complexion entirely."
Chile will now face Brazil at Johannesburg's Ellis Park in the second round on Monday.
As well as Estrada, they will be without Gary Medel and Waldo Ponce, who are also suspended after being booked against the Spanish.