Goals from debutant Andreas Cornelius, Nicky Maynard, Peter Whittingham and Craig Noone sealed the Premier League new boys' victory against their non-league opponents.
The hosts scored three good goals of their own through James Norwood, Danny Wright and Matty Taylor that are sure to have given Cardiff boss Malky Mackay some cause for concern.
The Conference Premier side briefly threatened but Nicky Maynard doubled Cardiff's lead soon after. Kim Bo-Kyung and Craig Conway worked a neat corner routine that led to the striker firing beyond Russell.
However, Forest Green pulled a goal back on the stroke of half-time as Norwood finally got his reward for some good play, the midfielder poking his shot past Joe Lewis' outstretched arm.
The hosts had the final say in the match as Taylor made no mistake after finding himself unmarked inside the penalty area, but Cardiff held on for the win.
