It took just seven minutes and the damage was done.
Callum Robinson's moment of madness will no doubt go down in South Wales derby folklore as one of the most brainless moments ever seen in this fixture.
Mark Hudson, perhaps after seeing this team accused of lacking passion in this fixture in the past, had previously stressed how much work had gone into emphasising the importance of this fixture to the players. But in that moment, whatever plans he had in place were very quickly in tatters.
Now, after some past optimism, there's a feeling Cardiff City's season is in real danger of going the same way.
After such a positive start to his stewardship, Hudson has endured a nightmare week that has yielded three defeats, two red cards and not a single goal. They're now 20th, and are currently more likely to be fighting a relegation battle than entertaining any notions of a top-six finish.
Derbies shouldn't define a club's season, and there was a notable feeling of dread among Cardiff fans in the build-up to this fixture. It's perhaps got to a point where Bluebirds supporters are almost expecting defeat.
But there are real problems that go far beyond an inability to cope with their friends down the M4. Problems that even Swansea City boss Russell Martin alluded to in his post-match press conference.
Hudson is the third Cardiff manager to face Martin in as many derby outings, and there's every chance there will be another face in the dugout when the two teams meet again later this season.
The club seemingly haven't been in any rush to address the managerial situation at the moment, but Sunday surely dealt a severe body blow to Hudson's hopes of taking the job.
Perhaps it's best to move on, but the decision to sack predecessor Steve Morison is looking increasingly difficult to justify at present. Despite the bright start, the new manager bounce has seemingly worn off already and, despite some signs of fight on Sunday, no one can seriously argue that this team is really looking any better under the current interim boss.
Hudson's remit was to try to play a more front-foot brand of attacking football, but after that positive opening trio of games, Cardiff's style and philosophy have looked muddled and disjointed at times.
Again, the sending off didn't help, but Cardiff just didn't look after the ball anywhere near well enough against the Swans, and there were even signs of the dreaded long-ball approach creeping back into the playbook.
Swansea captain Matt Grimes, typically magnificent in the middle of the park, completed more passes than the entire Cardiff team at the Swansea.com Stadium, a stat that arguably laid bare Cardiff's difficulties.
Perhaps it was a case of needs must. After all, it was a similar story at Queens Park Rangers in midweek. But after six games, Hudson's philosophy and style still seem difficult to define.
Injuries admittedly haven't helped him find the fabled 'best XI'. The likes of Rubin Colwill and Isaak Davies remain waiting in the wings after so long on the treatment table, while Mahlon Romeo, Perry Ng and Ebou Adams are all due to return to the fray.
A fully-fit squad may well change the dynamic, but there are certain players who quite simply aren't offering enough at the moment.
The likes of Sheyi Ojo and Romaine Sawyers, with all their experience at this level, simply haven't reached the levels many would have hoped for so far, while on current form Jaden Philogene won't be challenging for a start at parent club Aston Villa any time soon.
Up front, there remain doubts over the suitability of Max Watters in the Championship, while Kion Etete is yet to really make any sort of impact.
Getting a tune out of all them would present a huge boost to the depth of Hudson's squad, particularly with star striker Robinson out for the next three games.
But the lack of clarity over Hudson's own future remains the real elephant in the room. As long as the word 'interim' remains alongside his name, uncertainty will remain - and it's not doing anyone any good.
Bluebirds hero Danny Gabbidon is one of those to have come out and urged the hierarchy to make some sort of decision either way. On the eve of the derby, he told WalesOnline: "It's something that needs to get sorted out.
"Are you going to give it to him? Are you going to bring someone in? The longer that uncertainty goes on, it doesn't really help the players, it doesn't help Mark Hudson himself and you just want to get a bit of continuity so the players know what's going on, you can get your head down and start getting results."
Few Cardiff fans would argue with that assessment. Neither, it seems, would Swans boss Martin.
For all the unease around their American ownership, Swansea have undeniably established a clear and definitive long-term identity and philosophy, which largely dictates every decision made at almost every level.
You may disagree with how they do things, but there's a clear direction and plan there - and that's hugely comforting for those watching on from the terraces. It's partly why Martin was afforded so much patience last season.
Cardiff, in contrast, appear trapped in a vicious circle of short-termism and quick fixes, and there's every chance it may yet catch up with them.
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