Each of the goals for the five-time winners came in the first half as Vinicius Junior, Neymar, Richarlison and Lucas Paqueta all getting on the scoresheet.
While South Korea were overawed during the opening period, Alisson Becker was forced into two quality saves, the first coming at 2-0, but the goalkeeper was powerless to prevent Paik Seung-ho from scoring one of the goals of the tournament in the second half.
Brazil now progress through to a quarter-final showdown with 2018 runners-up Croatia, who overcame Japan on penalties earlier in the day.
If all the attention pre-match was on the return of Neymar after an ankle injury, it took just seven minutes for eyes to be focused on a sublime finish from Vinicius Junior.
After good work down the right from Raphinha, the Barcelona man's cutback found its way through to his fellow La Liga player, who took his time before placing a composed effort past Kim Seung-gyu and a couple of South Korea defenders.
Before the quarter-hour mark, Brazil had doubled their advantage. After Richarlison was felled inside the penalty area, Neymar stepped up to win the battle of wills with Kim, who was wrong-footed as the ball was rolled into the opposite corner.
To their credit, South Korea almost halved the deficit soon afterwards, Hwang Hee-chan sending a stunning 25-yard effort towards the top corner before Alisson made a brilliant save to tip the ball over the crossbar.
While the Asian nation continued to hold their own heading towards the half-hour mark, they would soon be blown away. Brazil's third was sublime, a team move ending with Thiago Silva picking out Richarlison with an intricate pass and the Tottenham Hotspur forward firing confidently past Kim.
In the 36th minute, it was four as Vinicius Junior picked out the run of Lucas Paqueta, who volleyed the ball into the bottom corner from 12 yards out.
Brazil had scored four goals in the first half of a World Cup match for the first time since 1954, but there was no let up in their play, only timely blocks from Kim denying Paqueta and Richarlison after they had been presented with space inside the area.
The chances kept coming after the break, Raphinha forcing Kim into yet another impressive stop when his toe-poked effort appeared destined for the far corner.
Kim was also equal to another shot from the winger shortly after the hour mark, denying him at the near post, before Alisson retained his clean sheet at the other end with a sharp one-handed save to deny Hwang, whose volley was heading into the bottom corner.
However, the shutout was taken away from him with 14 minutes remaining. After a free kick was only cleared to Paik who was waiting 30 yards out, the midfielder took a touch before firing a sensational strike past the helpless Liverpool man.
The closing stages saw both sides create opportunities, as well as third-choice Brazil stopper Weverton being given a surprise run-out, but the end result was never in doubt as Brazil go through to a date with Croatia on Friday.