Boro found themselves three goals down at half-time after goals from Callum O’Dowda, Mark Harris and Perry Ng.
The hosts did threaten to stage a late comeback as substitute Duncan Watmore pulled a goal back 14 minutes from time, before Rodrigo Muniz reduced the deficit further.
Still, it was too little too late as Boro suffered their fourth defeat of the season.
Here’s how each Boro player fared:
1. Liam Roberts - 5
Got a hand to Cardiff’s second goal but was left exposed for the goals. Had to be alert when the ball was played back to him a couple of times. 5 Photo: Alex Burstow
2. Paddy McNair - 4
Struggled positionally as Boro’s defence looked disjointed and was picked apart. Was replaced by Anfernee Dijksteel at half-time. 4 Photo: Getty Images
3. Dael Fry - 4
Was slow to close Harris down for Cardiff’s second goal and was hesitant when the visitors attacked in the first half. 4 Photo: Getty Images
4. Matt Clarke - 4
Looked ponderous on the ball and didn’t get tight enough to his man for Cardiff’s third goal. Subbed off in the second half. 4 Photo: Dan Mullan