Chile has only won one of its past six matches heading into the Copa America Centenario, which starts on Friday.
Chile's preparations for its Copa America title defense went from bad to worse on Wednesday after substitute Javier Hernandez led Mexico to a 1-0 victory.
Hernandez came off the bench to score an 86th-minute winner as defending Copa champion Chile crashed to back-to-back defeats following last week's shock loss to Jamaica.
With the game seemingly petering out for a draw in the final warm-up fixture for both teams at Qualcomm Stadium in San Diego, Hernandez sprung the offside trap and headed powerfully past Cristopher Toselli as Mexico's unbeaten run extended to 19 matches.