Chile sink Northern Ireland in Santiago
Striker Esteban Paredes scored the only goal of the match with a header at the back post from a corner after 30 minutes.
The Chileans, who will play in group H alongside Honduras, Switzerland and Spain, dominated possession but seldom threatened the Northern Irish goal.
Chile are due to play again later on Sunday, against Israel. Coach Marcelo Bielsa is expected to name a completely different starting line-up for that match.
Bielsa has narrowed his squad down to 24 players but needs to drop one more man before Tuesday, the FIFA deadline for naming definitive World Cup squads.