Oli - Otto UK's answer to Asos.com - racked up £3 million in sales over its first three weeks, smashing internal targets by £1m.
Womenswear has been its strongest category, accounting for more than 60% of sales. Of those, 12% came from Oli's exclusive designer tie-ups with Maria Grachvogel and Jasmine Guinness.
More than 50% of Oli's total sales to date have been generated by its website. The rest comes from its catalogue.
Otto UK has ploughed £25 million into the Oli venture, which started trading six weeks ago.
Otto UK business development director Neil Sansom said: "It is very promising because we've gone from zero brand awareness. We've only been trading for five to six weeks and we've exceeded our expectations."
Demand was so strong that Oli encountered some stock shortages and delivery issues during the first four weeks of trading.
Hitwise, which monitors internet traffic to websites, said Oli reached its highest traffic ranking for the week to July 28, when it was the 20th most-visited fashion website. This was at the height of a major marketing campaign that included print, TV and online ads to support Oli's launch.
It has since fallen back to about 35th position, while Next, Asos.com and Topshop continue to occupy the top three places.