The struggling Cheetahs secured a bonus-point 36-32 win in a high-scoring Super 14 encounter in Bloemfontein to all but end the Blues' play-off hopes.
But they required a final-quarter rally to seal victory after wing Rene Ranger and halfback Alby Mathewson put the Blues 27-22 ahead.
Replacement Philip van der Walt cancelled out that advantage and Waltie Vermeulen's converted score proved decisive.
The Cheetahs had held a comfortable 22-13 advantage at halftime thanks to South Africa flanker Juan Smith's third-minute try and further scores from wings Jongi Nokwe and Bjorn Basson.
Centre Isaia Toeava had responded for the Blues, first five-eighths Stephen Brett kicking their other eight points.
But when Ranger and Mathewson crossed it looked as though the Blues would go into their last two fixtures, against the Lions and the Chiefs, with their hopes of advancing intact.
But forward Van der Valt, on as a blood-bin replacement, had other ideas and Vermeulen's try opened up a nine-point gap.
Blues wing Anthony Tuitavake pulled a try back but Brett's missed conversion left them still needing a further try and a valiant push in stoppage time was thwarted.
The defeat leaves them seven points adrift of the final play-off place, occupied by the Reds, while the Cheetahs remain second from bottom after Australian side Western Force beat the rock-bottom Lions.
Scorers:
Cheetahs 36
Tries: Smith, Nokwe, Basson, Van der Walt, Vermeulen
Con: Bosman 2, Olivier 2
Pen: Olivier
Blues 32
Tries: Toeava, Mathewson, Tuitavake, Ranger
Con: Brett 3
Pen: Brett 2
HT: 22-13