Friendly: Cardiff City 0-1 Celtic
Celtic pair Joe Ledley and Adam Matthews enjoyed a happy homecoming to former club Cardiff as the Scottish side eased to a pre-season win.
Anthony Stokes scored the only goal of the game, rising between two Bluebirds defenders to power Emilio Izaguirre's cross beyond keeper David Marshall.
Cardiff could have taken a lead in the first minute when Jon Parkin broke clear, only to blaze over the bar.
After that the hosts struggled to create clear chances on Celtic's goal.
Joe Mason - one of four Cardiff players making their home debuts along with Don Cowie, Andrew Taylor and Aron Gunnarsson - had a penalty appeal turned down after appearing to be tugged back.
But Celtic should have doubled their lead on 56 minutes when Gary Hooper exchanged passes with Stokes before shooting, only to be denied by an excellent Marshall save.
Charlie Mulgrew then wasted a gilt-edged chance with a free header on the back post after a corner, only to blaze back across the face of goal with the net at his mercy.
The Bluebirds opened their pre-season preparations with a 1-0 win over Charlton Athletic in Seville, Spain.
After losing to Celtic on Wednesday night, Cardiff have two more pre-season friendlies.
The Champioship side will travel to play League One outfit Bournemouth at Dean Court on 23 July, with that match a 1300 BST kick-off, before they take on Italian side Parma at the Cardiff City Stadium on Saturday, 30 July with a 1500 BST kick-off.