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Pritchard beat Tunisian Rim Jouini 15-10 on points in her lightweight contest and now fights world No 2 Sofya Ochigava tomorrow (early Tuesday NZT).
Under boxing's rules, losing semifinalists both receive a bronze medal.
The Aucklander had a big third round, which she won 5-1, and that gave her enough of a cushion to get the job done against an opponent who had beaten her in their one previous meeting in Tunisia last year.
"The result is what we wanted and what we've been training for," Pritchard said.
She asked her trainer and husband Cameron Todd not to tell her the scores after each round.
"I think that was the best move because maybe I might have tensed up and tried to go in, which is exactly what I shouldn't have done."
Instead she kept moving against an opponent who tended to flail forward, leaving herself open to being picked off by the taller New Zealander.
Pritchard did ask the score before the fourth and final round. Told she was a few points up, she said her feet got "less jittery" and got through the last round comfortably, albeit despite going down once.
Pritchard's parents were in the crowd, along with friends who live in London.
"I'm just so proud of myself and proud to be a boxer. Cameron thought I'd make a good boxer; he's one of the reasons I'm here."
Pritchard rated boxing making its Olympic debut today as a great day for women in sport.
"There are many countries out there whose women still don't have equality in their lives and I think it's very unfortunate and sad," Pritchard, 28, said.
"I'm not sure this day will change that for certain countries but it's an absolutely great day for women out there to finally get in the ring and show what we've got.
"We're skillful and we deserve to be here."
As for Ochigava, she's seen her fight before, met her several years ago at a tournament and rates her "an amazing, skillful athlete".
"She's a southpaw and a counter boxer. I know what she does, so we'll have a game plan.
"I think she'll counter box and wait for me to make mistakes. But if I stay focused and stick to my guns I feel I have a very good chance," Pritchard said.
New Zealand's other boxer today, flyweight Siona Fernandes lost on points to a clever Bulgarian Stoyka Petrova, 23-11.
- David Leggat, NZ Herald