The Huyton fighter was handed a bye for the first round and victory against Kumar leaves him one win away from a medal, with both losing semi-finalists awarded bronze in Olympic boxing.
The third seed was impressive in the first two rounds, opening up a 16-9 lead, but was forced to hang on to that advantage in a tough final round as Kumar looked to salvage the bout.
But though the Indian won round three 7-4, it was not enough to stop the Brit from beginning his belated campaign with victory.
