Aron Gunnarsson opened the scoring in the 16th minute with a powerful shot inside the far post.
Joe Ralls scored Cardiff's second goal in the 20th minute before Gunnarson went on to add his second seven minutes later.
Trailing 3-0 at half-time, Newcastle pulled one back with a Shola Ameobi penalty in the 49th minute.
At 3-1, Slovenian striker Etien Velikonja added another goal for Cardiff with a simple finish.
The match finished 4-1 in what was a miserable afternoon for Newcastle.