Coutinho, who was recalled to the starting line-up after a couple of matches on the bench, then doubled the lead nine minutes brefore the break, bending a super free-kick over the wall and into the top left corner past a helpless Jo.
Danilo got his first international goal on the hour with a crisp strike from outside the box.
The match extended South Korea’s poor run, with the Asian side now having gone three games without scoring.
The friendly was Brazil’s last before they begin their qualifying campaign for the 2022 World Cup in March next year.
Reuters contributed to this report