Joe Ledley's powerful strike put the Bluebirds ahead on 31 minutes after Jason Koumas had hit the woodwork with a direct free-kick moments earlier.
Preston levelled after 62 minutes when Tyrone Mears finished from close range.
Koumas restored the lead 10 minutes from time with a superb free-kick, but substitute Sedgwick lashed home the equaliser in the dying moments.
Preston boss Billy Davies:
"I'd like to look at them again as I fell they were unjustified and I told the referee that after the final whistle.
"We passed the ball well and did a fantastic job and thoroughly deserved at least a point if not all three.
"I was very pleased with our overall play, it was a good performance and I'm delighted with how we went about it."
Cardiff: Alexander, Weston, Purse, Loovens, Barker, Koumas, Whitley, Ledley, Cooper (Parry 66), Jerome (Lee 58), Ricketts.
Subs Not Used: Cox, Ardley, Margetson.
Goals: Ledley 31, Koumas 80.
Preston: Nash, Alexander, Lucketti, Davis, Mears (Sedgwick 87), Davidson, Lewis Neal (Dichio 87), Jones, Nowland (Nugent 73), McKenna, Agyemang.
Subs Not Used: Ward, Mawene.
Booked: Davis, Mears.
Goals: Mears 62, Sedgwick 90.
Ref: H Webb (S Yorkshire).