It came in the eighth minute after a fine run from Jason Koumas had resulted in a corner. When the flag-kick came in Ricketts rose to head across goal and into the corner.
Leading scorer Mark De Vries fired in a shot that went high over the bar as the visitors mounted some concerted attacks in an attempt to get back on level terms.
Just on the half hour Rhys Weston was turned by De Vries, who then crossed into Cardiff's danger area. Keeper Neil Alexander failed to claim the loose ball but Darren Purse hammered it behind for a fruitless corner.
In the last minute before the interval Purse needlessly handled just outside the penalty area and in a central position Joey Gudjonsson's free-kick was a poor one that struck the wall before being scrambled clear.
In the 58th minute the match sprang into life as a melee started by Leicester full-back Patrick Kisnorbo threatened to escalate, but it was quickly brought under control by the referee who yellow-carded the Foxes defender.
The Bluebirds were now on top, but without looking like grabbing the second goal they needed, and when Cameron Jerome turned his man to raise Bluebirds hopes, his snapshot flew well wide.
Leicester used all three substitutes in an effort to turn the tide, but with Glenn Loovens outstanding for the home side there seemed no way through for the Foxes.
Iain Hume, so often a thorn in the Bluebirds' side when at Tranmere, began to worry the Cardiff backline and Loovens had to jump high to clear a dangerous cross field ball.
It was Hume who fired over a centre that was turned at the near post in the 83rd minute, but to Cardiff's relief it was disallowed for offside.
The Bluebirds were hanging on as the game drew to a close, with Dion Dublin now up front to add weight to the Leicester strikeforce.
A free-kick and a corner in the last minute of injury time were hacked clear and Cardiff hung on for their second victory of the season.