The Belfast Giants beat the Devils in Wales on Sunday night to complete a weekend Elite League double.
Jeff Mason put the visitors ahead late in the first period before goals from Aaron Clarke and Jeremy Rebek gave the Giants a 3-0 lead.
Phil Hill and Jeff Pierce netted for Cardiff but Adam Keefe ended hopes of a comeback by scoring Belfast's fourth goal with eight minutes left.
The leaders defeated Hull Stingrays 5-1 at the Odyssey on Saturday.
Brock McBride netted a double while Rebek, Clarke and Gareth Roberts were also on target for the Giants.