he sides were locked at 10-10 at the break. Former New Zealand centre Casey Laulala going over for the Blues while full-back Freddie Burns crossed for the Cherry and Whites. Ben Blair and Nicky Robinson kicked five points apiece.
But a hat-trick from Simpson-Daniel put the visitors out of sight, meaning Ceri Sweeney's late try was little consolation for Dai Young's side.
The away side made an assured start with former Cardiff fly-half Robinson being successful with one of two early penalties to open the scoring, but the Blues quickly hit back with a penalty of their own from full-back Blair.
Laulala made a clean break through the heart of the Gloucester defence and stepped Burns brilliantly to dot down under the sticks. Blair added the conversion.
But some ill-advised adventure from the home side allowed Gloucester to level the scores on the stroke of half-time. Sweeney looked to move the ball wide with a cut-out pass but it was picked off by Burns who sauntered over the line for a try converted by Robinson.
And Gloucester carried that momentum into the second half as, after Blues' flanker Ben White was sin-binned for slowing down the ball, they moved the ball right after a quick-tap penalty for Simpson-Daniel to get over out wide, Robinson producing a brilliant touchline conversion.
The Blues responded with a spell of pressure of their own and Blair kicked his second penalty to narrow the deficit to 13-17.
But that was as close as Cardiff got as flanker Akapusi Qera fed Simpson-Daniel for his second, and a Burns chip then gave the former England winger his treble.
Good work from Laulala put Sweeney in for a try two minutes from time. But it was not enough for the Blues, who now face a battle for Heineken Cup qualification through the Magners League.