Crystal Palace 0 Cardiff City 2
But Cardiff's win was marred by a half-time melee which spilled into the Selhurst Park tunnel.
The row started when Cardiff boss Dave Jones confronted Palace defender Claude Davis after the Jamaican looked to have caught Roger Johnson with an elbow which forced the Bluebirds defender off in the dying seconds of the opening period.
Jones and Palace boss Neil Warnock both failed to appear for the second half after being sent off by referee Russell Booth for their part in the unsavoury incident.
On the pitch, McCormack's first-half penalty and his super solo effort sealed all three points for Cardiff.
Michael Chopra had a effort ruled out for offside in the opening five minutes, before Julian Speroni made a good reaction save from Jay Bothroyd's thunderous free-kick.
Palace hit back with chances of their own through Shefki Kuqi and Rui Fonte, before McCormack sent Speroni the wrong way from 12 yards after Nathaniel Clyne clipped Joe Ledley in the box.
But the goal seemed to galvanise Palace, Stuart Taylor produced an outstanding save from Victor Moses' deflected effort, then Kuqi scuffed his shot when put through by the England Under-19 international, before the controversial half-time scenes marred an entertaining opening 45 minutes.
Ledley should have doubled Cardiff's lead after firing wide from McCormack's pinpoint free-kick in the 54th minute.
Nick Carle's dangerous inswinging free-kick caused havoc in the Cardiff box in the 74th minute as Palace searched for the equaliser.
But after an uncomfortable final ten minutes, McCormack eased any Welsh nerves with a brilliant solo effort to seal a 2-0 win for the away side.