London Irish face an anxious wait after they fell to a 10-6 LV= Cup defeat to Cardiff at Cardiff Arms Park.
After contributing to their own downfall with an error-strewn performance in Wales, the Exiles are now reliant on Worcester beating Saracens on Saturday if they are to reach the semi-finals.
The Blues were there for the taking with nine senior players on Six Nations duty with Wales, and visiting full-back Tom Homer slotted the first points of the game with a penalty midway through the first half.
Home fly-half Rhys Patchell then passed up the chance to level with a Cardiff penalty but played a big part in the build-up to the game's only try soon afterwards.
His well-placed grubber kick bounced awkwardly for the retreating Homer, who could only spill possession and allow Blues acting captain Gavin Evans to pounce and touch down - Patchell converting neatly.
Homer's misery was compounded as a second penalty moments before the interval rebounded off a post, and the hosts emerged for the second half determined to protect their fragile lead.
Guy Armitage served notice of Irish intentions with a scything break through the midfield, and Homer eventually cut the deficit to 7-6 when he booted through the posts to capitalise on a penalty from a scrum.
But having missed one chance to restore the breathing space, Patchell coolly knocked over a second and some valiant defence at the death denied Irish the try they needed to be sure of a place in the last four.