With this drubbing, India's chances of playing for fifth to eight spots is ruled out. They will now vie for places 11 and 12. India will finish last in Group B since Belgium have already got four points with one match left against India.
India's defence has been exposed throughout the tournament as they have conceded 15 goals and scored only five.
Jong Hyun Jang (6th minute), Hyun Woo Nam (59 and 70), Seung Il Lee (68) were the scorers for South Korea. India could not capitalise on their four penalty corners while South Korea struck thrice in five.
South Korea started off on a good note with a goal in the sixth minute. But India equalised in the ninth through Gurwinder Singh. After that rain came down at the Riverbank Arena during the first half but play continued. Both teams went to the break with the score 1-1.
However, in the second half, South Korea added two more goals while India failed to sound the board. South Korea's third goal came towards the end, in the 68th minute and in the final minute made it 4-1 via a penalty corner to hand a humiliating defeat for the eight-time Olympic gold medallists.
India, who are in Group B, have now lost to The Netherlands (2-3), New Zealand (1-3), Germany (2-5) and South Korea. Their last group stage game is against Belgium on Aug 7, Tuesday.