On a day of high emotion, as the hosts waved goodbye to a number of long-serving stars, Connacht looked set to give them a fitting send-off with tries from centre partners Matt Healy and Robbie Henshaw sending them clear.
But a dramatic final 25 minutes saw Blues suddenly click into gear in devastating fashion to leave the Irish province shell-shocked.
The visiting pack took control in the set piece to claim a penalty try and three minutes later an opportunistic score from scrum half Lewis Jones put Blues ahead.
In-form full back Dan Fish grabbed a third try after some stunning handling from Blues to cap a stunning comeback as the visitors closed the game out in some style to claim another league scalp as they chase down seventh spot.
Blues had made three changes to the side that defeated Scarlets on Judgement Day with winger Harry Robinson called up for Chris Czekaj and Lloyd Williams starting at scrum half.
The only change to the pack came at Number Eight where Ellis Jenkins started, while fly half Gareth Davies played his 50
th game for the region as Blues looked to build on a hat-trick of wins.
It was the boot of Davies and his opposite number that dominated the opening quarter of the game as both teams looked for territory to attack from under overcast skies.
Running rugby was at a premium, but when Blues did get ball in hand they looked dangerous as Wales ace Alex Cuthbert cut Connacht wide open with a searing break from deep as he stepped past tacklers.
Cuthbert’s floated long pass left to the supporting Fish saw the full back kick ahead, only for his nudge to have too much pace for the galloping Robinson to collect and touch down.
An early penalty from home full back Darragh Leader came back off the right upright before another electric break from deep saw Blues fire the ball through hands.
Macauley Cook and Robinson, on the angled run around, made space down the middle of the field before Fish again rattled into contact at pace. Connacht, though, held firm under intense pressure and won the scrum after Blues carelessly knocked on.
Dafydd Hewitt and Cuthbert were next to combine down the right flank with some neat offloads out of the tackle, but once again the home defence solidly held firm.
Another penalty, this time for playing the ball on the floor, handed Connacht the opening points of the evening as fly half Nikora confidently slotted the kick from in front of the posts.
The lead gave the home side crucial momentum and they looked to turn the screw, after another penalty at the lineout following a tackle in the air on scrum half Kieran Marmion, as Leader kicked for the corner.
The first drive from the hosts was easily repelled, but Connacht then broke through the middle as a neat grubber kick in behind was collected by a diving Healy and the conversion from Nikora put the hosts 10-0 ahead just before the half hour.
The Irish side suddenly had real zip about their attacking play as they went wide with pace before a high up and under from Nikora was taken by Robinson under huge pressure.
Blues were struggling to get going as Connacht started to dominate territory while the penalty count started to hurt the visitors who were pinned back.
Poor handling in their own 22 then gift-wrapped Connacht another attacking scrum six minutes before the break.
A free kick at the resulting scrum allowed the alert John Muldoon to take a quick tap and go and drive low for the whitewash. The home support thought he was over under the posts, only for the home skipper to be penalised for a double movement.
Blues looked to mount a charge before the interval after Danie Poolman’s clearing kick flew out on the full. Hewitt broke the defensive line as he stepped inside and a penalty, for pulling back off the ball by Henshaw, saw Gareth Davies kick to the corner.
The visitors flexed their muscles up front as they bulldozed up to the line to win yet another penalty. This time Davies opted for the three points as he slotted the kick to cut the lead back to 10-3 at half-time.
Blues made a half-time change, as Scott Andrews replaced Taufa’ao Filise, but yet another penalty for offside within 60 seconds of the restart gave Connacht early field position.
The home side rumbled ominously up to the line with only a superb tackle on powerhouse prop Rodney Ah You stopping the giant from close range as Blues were forced to dig deep and put bodies on the line.
The relentless home pressure told as the Irish side pounded at the door and finally found a way through as centre Henshaw found a gap to touch down from close range to extend the lead to 15-3.
Bradley Davies and Filo Paulo, with storming powerful runs up field, looked to spark Blues back into life, although Poolman was only inches from intercepting a pass that would have seen him clear as he flew out of the defensive line.
Blues needed a way back quickly before the game drifted away and twice turned down a kick at the posts after winning a penalty, instead opting to go for the corner and hunt the comeback try.
The second attempt saw Blues held up as they powerful drove over before a series of five-metre scrums saw them really apply the pressure and shunt Connacht back before the inevitable penalty try was awarded.
The game had suddenly turned on its head and Blues, from nowhere, were completely ion control and in the ascendancy.
More drama duly followed just three minutes later as a huge combined tackle in midfield by Josh Navidi and Scott Andrews dislodged ball.
Ellis Jenkins showed his range of skills as he hacked into space with no full back at home and Jones brilliantly won the foot race to the loose ball and touched down. Davies added the extras for the lead and the home crowd silenced.
Connacht looked to regroup and they won a sustained aerial battle for territory as former Blues man Dan Parks produced a sublime kick to the corner under pressure.
The hard-working front row duo of Matthew Rees and Gethin Jenkins were replaced with 13 minutes left, but Blues lost none of their control up front as another huge drive saw Aly Muldowney yellow carded.
Blues duly shunted the resulting scrum up field and some superb handling, as Cuthbert fired a pass out of the tackle, allowed Jones the space and time to throw a miss pass to Fish out wide who raced in the left corner for a 22-15 lead with ten minutes left.
Another yellow card for Connacht, against Eoin McKeon for a dangerous tackle on Hewitt, could not halt a grandstand finale from the hosts. But when Parks went for territory with a penalty he saw his kick run dead and with it any hope the hosts had.
A penalty at the scrum gave Simon Humberstone a long range kick to settle any nerves. But although his kick sailed left of the target it was only a matter of seconds before the final whistle signaled a fourth win on the trot.
Timeline:
22m Nikora p 3-0
26m Healy t Nikora c 10-0
40m Davies p 10-3
45m Henshaw t 15-3
56m Penalty t Davies c 15-10
59m Jones t Davies c 15-17
69m Fish t 15-22
Cardiff Blues: 15 Dan Fish, 14 Alex Cuthbert, 13 Cory Allen, 12 Dafydd Hewitt, 11 Harry Robinson, 10 Gareth Davies (Humberstone 64), 9 Lloyd Williams (Jones 55); 1 Gethin Jenkins (Davies 67), 2 Matthew Rees (Dacey 67), 3 Taufa’ao Filise (Andrews 40), 4 Bradley Davies, 5 Filo Paulo, 6 Macauley Cook, 7 Josh Navidi, 8 Ellis Jenkins (Hamilton 77)
Replacements: 16 Kristian Dacey, 17 Thomas Davies, 18 Scott Andrews, 19 Chris Dicomids, 20 Luke Hamilton, 21 Lewis Jones, 22 Simon Humberstone, 23 Isaia Tuifua