Rotherham interim manager Paul Warne apologised for their "embarrassing" 5-0 Sky Bet Championship defeat at Cardiff.
Goals from Kadeem Harris, Junior Hoilett, Craig Noone and a Kenneth Zohore brace gave the Bluebirds their biggest win since a 6-0 victory over Bristol City in 2010.
It leaves Rotherham, who were without the ineligible duo Semi Ajayi and Tom Adeyemi against their parent club, rooted to the foot of the table and 15 points from safety.
Relegation to League One is looking increasingly likely for the Millers and Warne pulled no punches in his assessment of their latest performance.
He said: "We knew what Neil Warnock's Cardiff were all about with their corners and long throws. So I was hoping my players would be man enough to defend them.
"Coming into this game, with the players we had missing, I was more hopeful rather than expectant of a result.
"But to get drummed like that was embarrassing for the club. The fans don't deserve that and I played a part in it so I apologise.
"Realistically we know where we are. But it's my job to prepare the team and hopefully give the fans something to be proud of."
The Millers failed to deal with Aron Gunnarsson's long throw and the ball fell to Harris who curled his effort past Richard O'Donnell in the 11th minute.
And when Hoilett doubled their lead thanks to a disastrous back pass from Ben Purrington, the game was all but over.
Warnock's men added a third strike in the 49th minute after Noone volleyed home Harris' looping cross.
Zohore then got in on the act with a second-half double to compound Rotherham's misery.
Despite a third successive win for Cardiff, boss Neil Warnock could not fully enjoy it against his former club.
Warnock took the Millers on an 11-game unbeaten run which saved them from the drop last term.
He said: "I was glad to see the second goal go in at half-time and even more happy to see the third one go in because I knew that was the killer.
"I didn't feel good about the game with it being my old club and the situation they're in.
"I've been there and I know how difficult it can be. So I do wish Rotherham well."
One negative for Cardiff, who stay 12th, was a serious-looking injury to Rhys Healey. The young striker was stretchered off just before half-time.
Warnock added: "Rhys Healey's injury soured everything really. We think he's done both his ligaments, which would be a major blow for him."