Eduardo Vargas scored a second-half brace to go with goals from Erick Pulgar and Alexis Sanchez as the two-time defending champions claimed a comfortable win in Group C.
Japan, who have taken a youthful squad to the tournament, had their chances but lacked a cutting edge.
Pulgar's header and Vargas' deflected strike set up the win, before the latter scored again after Sanchez's effort as Chile joined Uruguay on three points in the group.
Japan made the better start with Takefusa Kubo, signed by Real Madrid last week, central to their energetic opening.
Kubo curled a free-kick over in the seventh minute, before Naomichi Ueda headed a corner straight at Chile goalkeeper Gabriel Arias soon after.
Chile grew into the encounter as Sanchez fired two attempts off target just after the half-hour mark.
They would be rewarded for their period of dominance with the opener, Pulgar heading in a Charles Aranguiz corner in the 41st minute.
Japan almost responded immediately, but Ayase Ueda scuffed a shot wide from an angle after rounding Arias, while Sanchez headed a cross straight at Keisuke Osako at the other end on the stroke of half-time.
Chile doubled their lead nine minutes into the second half through Vargas, whose strike from the edge of the area took a deflection and went in after a Mauricio Isla cutback for his 37th international goal.
Again, Ayase Ueda squandered a chance to respond, firing wide at the back post after a cross from Gaku Shibasaki.
Kubo also had an opportunity after the hour-mark, bursting into the box before shooting into the side-netting from a slight angle as Japan looked for a way back into the game.
Instead, Chile sealed their win in the closing stages through goals from Sanchez and Vargas.
Sanchez headed in a cross from Aranguiz before playing in Vargas, who lobbed Osako after the goalkeeper's rash decision to rush out.
What does it mean? Winning start but work to do for Chile
Taking three points was the key for Reinaldo Rueda's men, but there is plenty of room for improvement. They started the encounter scrappily before building into it, which they will hope is a sign of things to come.
Vargas goes past Salas
Vargas has consistently delivered for Chile and his goals were his 37th and 38th at international level. He went past Marcelo Salas and into second on the nation's goalscoring list, moving within four of Sanchez (42).
Kubo shows glimpses for Japan
Most of Japan's good moments came thanks to Kubo, who signed a six-year deal with Madrid last week. He almost set up Ayase Ueda after a nutmeg down the left in the first half and his excellent touch and left foot showed why he has been described as the 'Japanese Lionel Messi', although he squandered a good chance in the second half.
Key Opta Facts:
- Chile are unbeaten in their past six Copa America games, winning five and drawing one.
- They have now won four of their past five opening Copa games.
- Chile have kept four consecutive clean sheets in the Copa America for the first time.
- Vargas moved onto 12 Copa America goals, which is the most for Chile ahead of Enrique Hormazabal (10).
Chile's campaign continues against Ecuador on Friday, while Japan take on Uruguay on Thursday.