Cardiff battled back from a nightmare start at Parc y Scarlets to claim a bonus-point victory and make it two from two in the BKT United Rugby Championship.
The Blue and Blacks were shellshocked as the Scarlets struck in fortuitous circumstances from the kick off and built a 15-point lead after a ruthless 11 minutes.
It appeared ominous for Matt Sherratt’s men but they showed an abundance of resilience to weather the storm, regather their composure and launch a fight-back.
They responded through tries from Liam Belcher and Mason Grady and trailed by just three points at the interval.
A dominant second-half performance at the set-piece laid the foundations for a Harri Millard try to take the lead and it was one Cardiff never surrendered.
Ben Thomas collected his own kick to secure a bonus point and Sheedy converted from wide to make it 15-24.
Cardiff were able to see the game out, although the home side missed a penalty in the 79th minute which could have set up a grandstand finish.
It took just 14 seconds for the Scarlets to open the scoring on their home patch as Tom Rogers athletically claimed a switched kick-off and burst into space.
The Wales back-three international attempted to kick ahead but his effort was charged down by Winnett. However, the ball unfortunately fell straight into the hands of Macs Page, who had been racing to get into support.
Sam Costelow added the extras and a penalty three minutes later to give his side a commanding early lead.
Things could easily gone from bad to worse when Winnett was harshly pinged for holding on and Costelow kicked to the corner but the Blue and Blacks held out the maul before repelling a number of big carriers.
It appeared as though they would eventually crash over but captain, Liam Belcher, provided an important moment of inspiration as he pounced for a try-line turnover.
However, it did not take long for the Scarlets to surge forward once more. The west Walians were playing with a pace and intensity that barely gave Cardiff the chance to take a breath. Eventually their pressure told and the ball was spread wide to Taine Plumtree for an easy run in.
Costelow was unable to add the extras but the home side were now leading 15-0 after just 11 minutes.
Cardiff restored some order as they claimed a try, through Belcher on 18 minutes. The opportunity was created after Ben Thomas and Mason Grady combined in midfield. It did not lead to a score but earned a penalty and after kicking to the corner the pack rumbled over.
Three minutes later it was the Blue and Blacks who claimed a quick-fire second and it was a fine team effort. Following a half break from Iwan Stephens down the left, Cardiff went on the attack.
Corey Domachowski received the ball at first receiver and released Sheedy with a beautifully delayed pass. Sheedy put Winnett away on a short line and while the full-back was almost ankle-tapped, he kept his feet and drew Ioan Lloyd to send Grady on a canter in.
Sheedy added the extras to make it 15-12 and very much game on following a difficult start.
The Scarlets continued to get the rub of the green an after loosing the ball at a mess breakdown they were able to hack through to set alarm bells ringing.
Winnett could do little to avoid conceding a scrum five but from the ensuing set-piece Johnny Williams knocked on with Thomas and teammates hitting hard.
Both teams had opportunities in a helter-skelter final few minutes of the half but the scores remained 15-12 entering the break.
Cardiff had opportunities to level the scores after Sheedy already bleeding from a cut took a high shot but they first kicked to the corner and then opted for a midfield scrum.
Sherratt’s side were given a third penalty when Ryan Elias made contact with the head of Ben Donnell but there was enough mitigation for referee Christopher Allison to downgrade to yellow.
The pack went back to scrum and following another two scrum penalties Alec Hepburn joined his front-row colleague on the naughty step. Cardiff eventually took advantage, spreading the ball left to replacement Harri Millard, who dived over.
It gave the Blue and Blacks the lead but Sheedy hit the uprights and the scores remained 15-17. The Scarlets could have quickly responded but Lloyd fluffed a simple attempt from in front.
Cardiff were dealt a blow when Belcher was next to receive yellow after making contact with the head of Johnny Williams but again there was plenty of mitigation.
They survived unscathed, following an impressive period of defence, which would please Gethin Jenkins and they soon stretched their lead.
A booming kick from Thomas put Lloyd under pressure, it looked as though he had knocked on but Allison waved play on and while the ball squirted through the hands and legs of Grady, Thomas reclaimed the ball and did enough to fend away three chasing defenders.
Sheedy slotted the touchline conversion and Cardiff now held a nine-point lead with 15 minutes to play.
With quarter of an hour remaining there was still plenty to do but feeling the pressure, Scarlets began making unforced errors and the Blue and Blacks controlled the kicking battle.
Cardiff were able to keep the home side at arm's length for the final minute through their kicking game, and although Scarlets were awarded a late penalty which would have taken them within a score, the kick sailed wide to assure the Blue and Blacks of the win.