Du Preez was outstanding for the Boks when he came on in the second half of their 73-13 mauling of Argentina on Saturday, proving he is a must for the next World Cup in 2015.
He currently plies his trade with Japanese club, Suntory Sungoliath, who have been the country's domestic champions for the past two years.
Some pundits questioned Du Preez's inclusion in the Bok squad, saying he will be short of form as the quality of rugby in Japan is not up to scratch with the rest of the world. His last Test came at the World Cup in New Zealand in 2011.
But Du Preez proved all the doubters wrong on Saturday, and in an interview with the Beeld website, he defended the quality of rugby in Japan.
"People say the rugby there is weak, but nobody really ever sees it. It's of a high quality. My club, Suntory, are influenced by Eddie Jones, who was involved there for a long time.
"I went there to escape the pressure and limelight, but it was one of the happiest decisions I've made in my life. Japan changed my life completely. My family and I are learning so much... my rugby is different nowadays, my life is different.
"I've learnt a lot at my club. It was the best decision for my rugby and for me as a person. The Japanese culture gave me a new sense of values of respect and patience.
"The pace against Argentina was a lot similar to the rugby in Japan."
Du Preez has not travelled with the Boks to Mendoza for Saturday's Test there as he will only be available for the home games in the Rugby Championship. He was replaced in the squad by Piet van Zyl.