Whittingham brilliantly finished off a Paul Parry cross just before half-time and Michael Chopra added a second from the penalty spot just after the break.
A minute later Graham Alexander gave Preston hope from the spot only for Roger Johnson to then head in a third.
Whittingham helped seal the win with a great piece of skill before crossing for Chopra to score his second.
Preston boss Paul Simpson:
"It's a massive disappointment. We totally let ourselves down with that second half defensive performance - as a team not just as a back four. "It's easy to blame three games in six days, but I'm not going to blame that, that would be easy, but we got punished tonight because we didn't do our jobs properly.
"Fortunately we've got a long time before the next game and we've got to get it out of our system."
Cardiff: Forde, McNaughton, Loovens, Johnson, Ledley, Whittingham, McPhail, Parry, Scimeca, Thompson (Byrne 87), Chopra (Green 87).
Subs Not Used: Flood, Blake, Gunter.
Goals: Whittingham 44, Chopra 52 pen, Johnson 54, Chopra 67.
Preston: Lonergan, Alexander, St. Ledger, Chilvers, Hill, Pugh, Whaley, McKenna, Pergl, Nugent (Mellor 46), Dichio (Agyemang 61).
Subs Not Used: Henderson, Sedgwick, Wilson.
Booked: Pergl, Chilvers.
Goals: Alexander 53 pen.
Att: 12,889
Ref: T M Kettle (Rutland).
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