Thomas Christiansen's men arguably played their worst half of football since he arrived at Elland Road in the summer, with the Bluebirds capitalising on some mistakes from the Whites to take a 2-0 lead at the break.
Leeds' task of getting back into the game was made even harder as Cooper was dismissed shortly before the break after receiving two yellow cards.
The first for the defender came as he appeared to lunge into a challenge with both feet off the ground. Kevin Friend only cautioned the Whites skipper - seemingly because he got a decent amount of the ball while his back leg appeared to be bent back enough to take some of the edge out of the tackle - despite the apparent protests from the Cardiff players.
However, he was not on the pitch for much longer as a late challenge on Nathaniel Mendez-Laing saw Cooper - who was called up to the Scotland squad this week - dismissed for a second yellow.
The former Chesterfield man's reaction after making the challenge gave away that he knew what was coming - and unsurprisingly, there was little protest from anyone wearing white as the red card came out.
And Couzens took to Twitter at half-time to comment on Leeds' first-half display - which saw the Whites fail to test the Cardiff goalkeeper - and the captain's red card.
Out fought that half 2 silly bookings from coops we need more in midfield for me I think we will see lasogga and siaz now as well— andy couzens (@andycuz23) 26 September 2017