The unbeaten home side – who top the pool with a home quarter-final – looked in complete control after an exhilarating opening half saw them take total control with tries from Rob Buchanan, Jack Clifford, Marland Yarde and Ross Chisholm.
But from the apparent comfort of a 28-0 lead, the home side were left reeling after a stunning second half show from Danny Wilson’s men threatened the most incredible of comebacks.
Cardiff Blues roared back in style with tries from Cory Allen, Dan Fish and Lloyd Williams to spark hopes. And when Fish grabbed his second of the game the lead was dramatically cut to five points.
A late Ben Botica penalty settled any home nerves, but there was much for Wilson to be pleased about with his team still in with a fighting chance of a place in the quarter-finals if other results go there way on the final weekend.
Quins flew out of the traps with full back Brown making yards before Nick Evans almost picked out Marland Yarde with a cross field kick, but Fish mopped up and conceded a five-metre scrum.
The resulting scrum forced another penalty and, after England scrum half Danny Care was just short with a tap and go, it was Buchanan who eventually touched down from close range for a fifth minute lead.
Blues looked to respond as they went wide at pace to try and set Cuthbert clear before Allen led a counter attack from deep but his pass failed to find Blaine Scully up in support on his shoulder.
The home side, though, were repeatedly and dangerously looking to kick to the corner from penalties and it paid off when a driving maul was stopped only for home flanker Clifford to burst through a gap and score unopposed.
Another rally saw Vosawai rumble up the middle to go close before the ball was worked to Dacey who also came inches from the whitewash before the penalty went against Wilson’s men at the breakdown.
Quins started to open up with a slick offloading game breaking the advantage line time and time again before the forwards muscled up, took the ball up and pressure finally told as wing Yarde broke over for a 21-0 lead.
The visitors continued to try and throw counter punches as Dacey burst up the middle to win a penalty that Williams tapped quickly and almost raced away before being hauled down.
Home star Brown was then inches from his opening try as more power forced Blues back before the England full back dropped the ball as he stretched for the line.
But there was no let-off as one last attack from Quins saw them wrap up the bonus point on the stroke of half-time as Evans attacked from deep, spotted the space and grubber kicked in behind for wing Chisholm to pick up and dot down.
A bright opening to the second half from Cardiff Blues saw Fish break down the right wing but his final pass inside failed to find hands when a try looked certain.
However, seconds later the visitors did strike as a neat scrum move saw Cuthbert, Cook and Dacey all go close before Allen cut a sublime line to collect the pass from Williams at pace and crash in under the posts to cut the lead.
Six minutes later they scored again as Dillon Lewis and Fish made the initial inroads before Dacey rattled to the line and a flat pass from Williams picked out Fish on his own out wide to score.
Quins stemmed the flow of points with a penalty from Evans, after winning a scrum penalty, before Gareth Anscombe made his long-awaited comeback on 56 minutes as he replaced Scully.
Anscombe almost produced a moment of magic immediately as his flat miss pass picked out Lee-Lo, but the Samoan was adjudged to have lost the ball forward as he looked to slide over.
Cardiff Blues were now camped in the home half as they kept the phases going and Patchell looked to go in out wide but was shunted into touch.
The third away try, though, did come on 68 minutes when, after bad lineout ball, Williams picked up, rolled out of tackles, evaded several men and brilliantly scored a superb solo.
The home side suddenly looked rattled by the points being piled up against them and the fourth try came moments later as another cutting pass from Patchell this time found Fish to race down the left touchline and score.
A fast a frenetic final few minutes saw Lee-Lo again look to burst away from deep as home fans held their breath, and even a last minute penalty from Botcia could not deny Blues a point they so richly deserved.
Calvisano await on the final day… and hopes remains.
05m Buchanan t Evans c 7-0
12m Clifford t Evans c 14-0
23m Yarde t Evans c 21-0
39m Chisholm t Evans c 28-0
44m Allen t Patchell c 28-7
51m Fish t 28-12
56m Evans p 31-12
68m Williams t Patchell c 31-19
73m Fish t Patchell c 31-26
Cardiff Blues: 15 Dan Fish, 14 Alex Cuthbert, 13 Cory Allen, 12 Rey Lee-Lo, 11 Blaine Scully (Anscombe 56), 10 Rhys Patchell, 9 Lloyd Williams; 1 Sam Hobbs (Davies 33), 2 Kristian Dacey (E Lewis 62), 3 Taufa’ao Filise (D Lewis 48), 4 Macauley Cook (Reed 48), 5 James Down (Cook 53), 6 Josh Turnbull (Dolan 55), 7 Ellis Jenkins, 8 Manoa Vosawai
Replacements: 16 Ethan Lewis, 17 Thomas Davies, 18 Dillon Lewis, 19 Lou Reed, 20 Cam Dolan, 21 Tavis Knoyle, 22 Gareth Anscombe, 23 Gavin Evans