The Blues lost in controversial circumstances at the Brewery Field as the Warriors gained a try through departing skipper Gareth Thomas that clearly shouldn't have been allowed.
The centre placed the ball a metre short of the Blues' line and the referee had apparently already signalled that as a try before a double movement scraped the ball to the edge of the whitewash.
Three minutes later an apparent penalty try in favour of the Blues was not given and after that the Warriors held on in a thrilling encounter.
A single bonus point keeps the Blues in contention for Heineken Cup qualification if they gain maximum points against Edinburgh Rugby next week and the Ospreys lose their final two games.