The Bluebirds had entered this game third in the Championship, a point behind Norwich with both sides having two games to play.
But their hopes of putting pressure on the Canaries were dashed as a woeful first-half display saw Boro open up a 3-0 lead inside 21 minutes as Leroy Lita's 99th career goal and further strikes from Barry Robson and Richard Smallwood put Tony Mowbray's men in total control.
The result condemned Cardiff to their heaviest home loss since their final match at Ninian Park against Ipswich in April 2009, and meant that Norwich's win at Portsmouth sealed their promotion at the expense of the Bluebirds.
Cardiff look set to face another play-off campaign, unless the FA elect to mete out a heavy punishment to QPR over their signing of Alejandro Faurlin when the outcome of that disciplinary process is announced later this week.
Cardiff boss Dave Jones had named an unchanged starting XI from the win at Preston, although goalkeeper Stephen Bywater was fit enough to claim a place on the bench.
Stephen McManus and Tony McMahon were both fit to return from ankle injuries for the visitors as Jason Steele started in goal.
The Bluebirds got off to a nightmare start as McMahon's long diagonal ball found Lita, and the striker's well-placed header beat the despairing dive of Tom Heaton to find the corner of the net with less than three minutes played.
Cardiff sought a quick response with captain Craig Bellamy's cross just evading JLloyd Samuel, but moments later they were 2-0 down as their hopes of automatic promotion continued to fade.
Lita was given far too much space on Middlesbrough's right-hand side and his measured pass allowed skipper Robson to guide the ball into the far corner after 13 minutes.
And the game was as good as over after just 21 minutes as Boro found the net for a third time.
A neat exchange between Robson and Marvin Emnes sent the striker into space. Enmes cut in from the right to pull the ball back and find Smallwood for the midfielder to fire beyond a flat-footed Heaton to the astonishment of the home support.
Cardiff almost found a way back into the game on the half-four mark as a defensive slip allowed Jay Bothroyd space, but the striker's effort was tipped away by Steele.
Jones then sent Jason Koumas on for Samuel knowing his side were in desperate need of a creative spark but they remained frustrated, particularly after Bellamy was adjudged offside after lobbing home.
Cardiff were booed off at the interval but Kevin McNaughton almost gave them a lifeline early in the second half as he turned a Bellamy cross wide at the far post, and Bellamy was the creator again as Bothroyd flashed wastefully off-target from the edge of the box.
Smallwood and Kevin Thomson were both booked for clumsy tackles before Emnes also saw yellow as he made his way slowly from the field when substituted on the hour.
Michael Chopra came off the bench for the final 20 minutes before Chris Burke drove agonisingly wide, but the hosts' pressure ultimately came to nought.