Borgohain, the lone Indian boxer in action on the day, prevailed 3-2 over her rival who is 12 years her senior. Both the boxers were making their Games debut and the Indian became the first from her nine-strong team to make the quarterfinal stage.
The 23-year-old showed great poise in a tense contest to triumph by the thinnest of margins. She claimed all the three rounds on split points.
The 35-year-old Apetz was first German woman to qualify for a boxing event at the Olympics and also a two-time world championship bronze-medallist and a former European champion.
Borgohain is a two-time World and Asian championships bronze-medallist.
The youngster from Assam was the aggressor in the opening round before she changed strategy to play the waiting game.
The strategy worked out just fine despite the German’s well-placed jabs often troubling the Indian.
Borgohain relied mostly on her left hooks to keep the slender edge.
Apetz is a pioneering name in German boxing. She is pursuing a PhD in neuroscience, which she put on hold for a year to prepare for the Olympics.
Apetz made the Games cut after reaching the semifinals of the European Qualification Tournament last year.