Llanelli Scarlet brought the Blues' winning run to an abrupt halt at Stradey Park on Saturday, notching up an emphatic 38-10 to win leave their compatriots' title aspirations hanging by a thread.
The league leaders found themselves chasing the game from the start and now need to beat fellow contenders Leinster at the Arms Park in their final match next Friday and hope Ospreys slip up to have any chance of landing the silverware.
David Young's side were second best for long periods of an entertaining contest, but did manage to haul themselves back into contention thanks to a second-half try from Kiwi number eight Xavier Rush.
However, an 80-yard interception from replacement wing Barry Davies on 67 minutes turned the game on its head with Davies and Matthew Watkins racing in for further tries for the home side in the closing minutes.
The Scarlets took early control of proceedings thanks to a fifth-minute penalty by fly-half Stephen Jones and then a glorious try scored by left wing Watkins.
Much of the credit for the score went to the home pack, who shoved the Blues eight off a scrum on their own feed on halfway.
With the Blues defence on their heels, the ball arrived quickly in the hands of dangerous Kiwi centre Regan King, who then ghosted clear of opposite number Jamie Robinson before finding Watkins on his outside 25 metres out.
The second-highest try-scorer in the league's history needed no second invitation and crossed in the corner without a hand laid on him.
Jones missed with the touchline conversion, although the Wales skipper made no mistake with a 20th-minute penalty as the Scarlets extended their advantage to 11-0.
The Blues' woes increased when Wales and Lions flanker Martyn Williams was shown yellow 10 minutes before the break for an infringement at the breakdown in the shadow of his own posts.
Jones landed his third success and the lead was starting to look ominous for Young's men.
But despite soaking up plenty more pressure, they managed to get into half-time without any further damage.
Young brought on international fly-half Nicky Robinson at the break and he was immediately on the scoreboard with a penalty three minutes after the resumption.
His chance arrived after prop Iestyn Thomas became the second player to be sin-binned for another penalty at the contact area.
But moments after clawing back three points, the Blues gave away another soft penalty to Jones who made no mistake from 35 metres out.
The visitors then spurned a golden opportunity when wing Chris Czekaj was put clear, but ignoring Jamie Robinson on his shoulder, he chose the ambitious pass to right wing Rhys Williams - who spilled the chance with the line at his mercy.
The Scarlets were reduced to 13 men when lock Scott MacLeod was shown yellow for pulling down a lineout and the Blues finally took advantage on 56 minutes when former All Blacks number eight Xavier Rush stretched over the line from a close-range scrum.
Robinson was successful with the conversion and suddenly the lead was down to seven points.
With tension mounting Jones missed a long-range penalty and then came Barry Davies' critical interception on 67 minutes.
It looked almost certain that the Blues were going to score with three men clear out wide.
But Rhys Williams could only direct his pass into the arms of replacement Davies, who raced 80 yards unopposed to the line, to the delight of the home fans.
Jones's conversion made the cushion 14 points again and the relief around the ground was tangible.
It was a score which also knocked the stuffing out of the visitors with replacement Davies and Watkins touching down for their second tries of the game in the dying minutes to claim a bonus point and move the Scarlets back into fourth in the table.
It also kept the Magners League title race on a knife edge until the final weekend of the season.
For Llanelli Scarlets:
Tries: Watkins 2, B Davies 2
Cons: S Jones 3
Pens: S Jones 4
For Cardiff Blues:
Llanelli Scarlets: 15 Morgan Stoddart, 14 Darren Daniel, 13 Regan King, 12 Gavin Evans, 11 Matthew Watkins, 10 Stephen Jones, 9 Dwayne Peel, 8 Alix Popham, 7 Gavin Thomas, 6 Simon Easterby (capt), 5 Scott MacLeod, 4 Vernon Cooper, 3 Deacon Manu, 2 Matthew Rees, 1 Iestyn Thomas.
Replacements: 16 John Davies, 17 Ken Owens, 18 Adam Jones, 19 Dafydd Jones, 20 Clive Stuart-Smith, 21 Ceiron Thomas, 22 Barry Davies.
Cardiff Blues: 15 Ben Blair, 14 Rhys Williams, 13 Jamie Robinson, 12 Tom Shanklin, 11 Chris Czekaj, 10 Nick Macleod, 9 Mike Phillips, 8 Xavier Rush (c), 7 Martyn Williams, 6 Scott Morgan, 5 Deiniol Jones, 4 Bradley Davies, 3 Gary Powell, 2 T R Thomas, 1 Gethin Jenkins.
Replacements: 16 Scott Roberts, 17 Gareth Williams, 18 Mark Lewis, 19 Robin Sowden Taylor, 20 Wayne Evans, 21 Mark Stcherbina, 22 Nicky Robinson.
Referee: Tim Hayes (WRU)
Touch judges: James Jones (WRU), Jon Mason (WRU)