Ankush defeated Germany's Nick Bier 3-2 to score a gritty win and become the first Indian boxer to make the last-16 stage of the ongoing edition.
The 18-year-old is now two wins away from assuring himself of at least a bronze medal.
Earlier in the tournament, another Asian silver-winner Ashish (64kg) had made the round of 32 along with Sachin (49kg) and Reyal Puri (81kg), also an Asian medallist.
However, Anwar (52kg) and and Etash Khan (56kg) bowed out following second-round losses.