The menswear venture, which boasts labels including Diesel and Versace, took in more than £3,000 on Saturday's launch day alone.
Items for sale include a Dior Homme shirt from the winter 2005 collection at £49.99 and woollen Prada trousers at £69.99.
"It's been absolutely phenomenal," said Diane O'Brien, area manager at Oxfam. "You could not put a pin between the people all day on Saturday. They nearly cleared us out. It's about supply and demand now. If we can get the stock, they're going to buy it.
"This doesn't look like a charity shop, and that's my whole aim. We're not about slinging things out in buckets and boxes any more."
She added that Oxfam would expand the menswear concept if success continued.
Barney Tallach, deputy trading director at Oxfam, said "seven years of price deflation" caused by discount retailers such as Matalan, New Look and Primark had forced many Oxfam shops to differentiate their clothing.
Lekha Klouda, executive secretary of the Association of Charity Shops, said takings were "pretty special". "For a single day, £3,000 is a very high sales achievement," she added.
"For the sector as a whole, diversification and niche marketing is going to be increasingly important."
The shop's 18-month lease has been provided by an anonymous benefactor.
Volunteers, including students from the London College of Fashion, are staffing the shop.