Tom Shanklin (left) scored twice for the Blues
Saracens (22) 29
Tries: De Vedia, Johnston
Cons: Jackson 2
Pens: Jackson 5
Cardiff Blues (15) 40
Tries: Stcherbina, Shanklin 2, Lewis, Luveitasau
Cons: Blair 3
Pens: Blair 3
Cardiff Blues fought back from a 22-15 half-time deficit to end Saracens' interest in the EDF Energy Cup.
Ex-Saracens centre Tom Shanklin scored two tries for the visitors, who also went over through Marc Stcherbina, Mark Lewis and Mosese Luveitasau.
Full-back Ben Blair kicked 15 points in an assured display.
The home side scored tries through Ben Johnston and Tomas de Vedia, while Glen Jackson kicked 19 points, but they were outclassed by their Welsh opponents.
The defeat ended a miserable week for Saracens, who have become embroiled in a club v country row over which position former Great Britain rugby league captain Andy Farrell should play.
Farrell came on for the last 21 minutes at blind-side flanker but could do little to stem the tide as the Blues went back to the top of the group B table as the only side with two wins out of two.
The Cardiff side started quickly and took a 12-3 lead as Stcherbina and Shanklin crossed either side of a Jackson penalty for Saracens.
The hosts responded with a well-worked try of their own when winger de Vedia crashed over in the corner after good work from his forwards.
Jackson converted from wide out and he exchanged penalties with Blair to make it 15-13 to the Blues after 25 minutes.
Three penalties from Jackson gave the hosts a seven-point lead at the break but they were blown away in the second half.
Tries from Lewis and Shanklin helped the Blues into a 27-22 lead.
Then, after Blair added his third penalty, they pulled well clear when Luveitasau intercepted Johnston's pass - intended for Farrell - and cruised over.
Blair's conversion made it 40-22 before Johnston added a late consolation try for Sarries.
Saracens director of rugby Alan Gaffney
"I had an affable discussion with Andy Robinson and at an appropriate time Andy Farrell will get an opportunity at 12."
Cardiff Blues Dai Young (on two-try hero Tom Shanklin)
"I thought every time he had the ball he looked powerful and he looked like he could do something and in defence he put in a couple of hits.
"It augurs well for Wales in November."
Saracens: Haughton, De Vedia, Sorrell, Johnston, Ratuvou, Jackson, de Kock, Lloyd, Byrne, Visagie, Fullarton, Raiwalui, Chesney, Seymour, Gustard.
Replacements: Mercey for Visagie (75), Farrell for Chesney (60). Not Used: Cairns, Russell, Dickens, Laidlaw, Penney.
Cardiff Blues: Blair, Czekaj, Shanklin, Stcherbina, Luveitasau, N. Robinson, Phillips, Jenkins, Thomas, G. Powell, Jones, Sidoli, Morgan, M. Williams, Lewis.
Replacements: Evans for N. Robinson (70), Macleod for Phillips (73), Yapp for Jenkins (69), Goodfield for Thomas (73), Davies for Jones (69), Rush for Lewis (47). Not Used: Flanagan.
Sin Bin: Thomas (35), Davies (70).
Ref: Tony Spreadbury (Bristol).