Cardiff 1-3 Brighton
Two goals from Ashley Barnes and a late Will Hoskins strike maintained Brighton's 100% start and ended Cardiff's perfect record.
Barnes capitalised on a mistake to score Brighton's opener with a 30-yard effort on 39 minutes.
The striker doubled his side's lead from the penalty spot on 63 minutes after Craig Mackail-Smith was fouled.
Hoskins wrapped up the win before Peter Whittingham scored a last-minute penalty for the hosts.
Cardiff boss Malky Mackay was forced to make one change to his side with Joe Mason replacing the injured Aron Gunnarsson. Matthew Sparrow for Will Buckley was the only change to the Brighton line-up.
Brighton dictated the play early on and Barnes found the back of the net after six minutes, only for it to be ruled out for offside.
The home side settled into the game and created a few openings, notably from Robert Earnshaw and Craig Conway.
So it was against the run of play when the visitors went ahead on 39 minutes. Barnes picked up a wayward pass from Kevin McNaughton before unleashing a shot from 30 yards which caught David Marshall by surprise.
Six minutes into the second half another Cardiff defensive mistake, this time by Anthony Gerrard, presented an opportunity for Craig Mackail-Smith, but the striker's shot from close range hit the post.
The visitors were awarded a penalty on 63 minutes following Mark Hudson's foul on former Peterborough striker Mackail-Smith.
Barnes's right footed spot kick sent Marshall the wrong way.
Cardiff found it hard to break down a resolute Brighton defence and it was no surprise when Brighton wrapped up the victory with three minutes remaining as Mackail-Smith's pass found Hoskins, who made it 3-0.
Cardiff's consolation came when Liam Bridcutt fouled Miller and Whittingham scored from the penalty spot.