The slimly-built Paarl athlete ran a personal best time of 57.91 seconds in the A-final on Monday.
“The best moment of my life,” she said afterwards with the national flag proudly draped over her shoulders.
“This medal is so precious, no-one’s going to touch it right now. I’ll be sleeping all night with it.”
There was some anxiety as the Games went into the ninth day of competition with no medal for the South Africans and Magerman said she had felt it her build-up.
“This was definitely one for the team. Coach Chris [White] just told me to go out and have fun but I was very aware of the fact that this would be our first medal, which makes it even more special.”
Going through the last bend and into the home straight she was lying seventh and then fifth then surged ahead for a comfortable victory.
Runner-up Michaela Perskova of Slovakia was clocked at 58.26 while the second fastest qualifier, Ellen Demes of Germany, walked crying down the tunnel after a fall going into the home straight.
Magerman said she could not explain her slow start but she never doubted herself during the race.
“I did have a slow start but I don’t really know why,” she said.
“I lengthened my strides from about 300m, probably because I didn’t want to fall over a hurdle, and then going around the final bend I kept on remembering how many times I’d practised that final bend with Chris and then I just pushed hard for the line.
“To be honest, although I knew I was quite far back in terms of position I never thought I wouldn’t catch them.”
The Grade 11 La Rochelle pupil from Paarl also gave credit to her coaches back home, Marna van der Burgh and Ronya Bosch while White fought back the tears in Nanjing.
“This is just the best feeling ever and making it that much more satisfactory is that we were the first code to win a medal for South Africa,” White said.
“I’ve worked with Gezelle since May at the African Youth Games but here my job was mainly to oversee her programme, fine-tune here and there and mostly to just manage things smoothly.”
Also in medal contention were the boys’ hockey side who have punched above their weight to reach the semi-final in the five-a-side version of the game.
They missed out on a place in the final as Australia went through 4-3.