In a stunning victory for the burgeoning fashion retailer, a top judge said the public would not likely be confused between ASOS's 'cool' clothes, targeted at '20-somethings', and Assos' costly lycra kit - which noone would expect to wear walking down the street without heads turning.
Switzerland-based Assos has been going since the 1970s and is famed for having produced the first pair of the now ubiquitous lycra cycling shorts.
Establishing a £14 million turnover with the world's cycling elite - the word 'assos' means 'the best' in Greek - Assos sells its shorts at about £200-a-go and its other products cost much more (see world's most expensive bib short).
Providing clothes to various national cycling teams, including the Russian cycling federation, Assos has clothed more than 250 gold medal winning cyclists in the Olympics and other international championships since the mid-1970s.
But it is a relative corporate minnow compared with Asos which, since the late 1990s, has established a massive internet presence, boasts almost 14 million customers and, in 2012, achieved a turnover of almost £500 million. It is valued on the stock market at around £2 billion.
At the High Court, Assos and its boss, Roche Maier - whose father, Toni, founded the business - accused Asos of breaching its trade mark, confusing the public and 'swamping' its goodwill.
However, Mr Justice Rose ruled there was little chance of confusion between ASOS wares and Assos cycle kit, including sleek bib shorts and skin-tight body suits which, whilst waterproof and aerodynamic, were "not garments that a man or woman could expect to wear walking down the street without causing heads to turn".
The history of the two firms could hardly be more different, with ASOS - an acroynym for 'As Seen on Screen' - taking its inspiration from celebrities and targeting 'cool, fashionable, on-trend' youngsters and Assos focused on the elite end of the cycling world.
ASOS had never sold technical cycling gear and, although Assos also had a range of branded casual wear and toiletry products, its goodwill was rooted in its reputation as a maker of premium cycling apparel.
Despite market surveys, reams of statistics from Google, and even evidence drawn from a 'prize draw' in a national newspaper, the judge said Assos had failed to prove that there was any 'actual confusion' between the two brands in the minds of average consumers.
Assos's reputation lay within the cycling fraternity, not the general public, and the judge rejected the company's plea that its trade mark rights were being 'swamped' and diluted by the worldwide success of ASOS.
Dismissing Assos's case, the judge said ASOS had, 'albeit belatedly', taken steps to guard against any confusion by ensuring that it does not promote goods bearing the ASOS name that directly relate to cycling.