Centre Jack Roberts scored twice for Llandovery while No. 8 Deri Mattravers crossed for a brace for Bedwas as both sides opted for attack instead of defence.
Llandovery had led 19-17 at the break, Roberts, James Garland and Lee Rees with their tries. Bedwas had taken the lead through an Ethan Davies score while Mattravers had also scored his first of the day.
But after the break, it was try after try in a breathless second half, Llandovery eventually prevailing by the narrowest of margins.
Roberts added his second try and there were scores for Aaron Warren and Chris Knight with Garland kicking the rest of the points.
Lewis Hudd, Lewis Robling and Mattravers' second were Bedwas' response but it was not enough.
It had been a super start for the home side, Davies slicing through for a try with barely a minute on the clock. The young fly-half added the conversion and with a stiff breeze in their favour, Bedwas would have been hoping there was more to come.
Davies put a long range penalty narrowly wide but it was not long before the Drovers got back into things. A Bedwas backs move broke down in midfield, Roberts making the most of things to pick up and canter in from 50 metres.
The conversion was missed but after falling behind so early, Llandovery were now firing on all cylinders. Spell after spell of sustained pressure saw them pound the Bedwas line, with Garland darting over to the right of the posts. Garland, who had replaced Cerith Rees at outside half for Llandovery, kicked the conversion before full back Lee Rees added a third score for the men in green.
Garland's conversion made it 19-7 and with Llandovery dominant, Bedwas were then dealt a further blow when fly-half Davies was forced off clutching his thumb. Will Owen replaced him, a move which coincided with Bedwas crossing for their second try of the day.
The ball was moved right at speed and with an overlap out wide, veteran No. 8 Mattravers powered over for what was the fifth try of an entertaining first half. Robling converted and added a penalty on the verge of half time to send his team in two points behind.
If the first half had been hectic, it was nothing compared to the second as both sides went try crazy, securing a bonus point apiece in double quick time.
It was Bedwas who scored first, Hudd scoring in the corner before an ill-advised chip from Garland found the hands of Robling who was left with an easy finish. He converted both scores and at 31-19, Bedwas looked like they had everything in their favour.
But Roberts soon crossed for his second try, Garland converting and kicking a penalty before Mattravers added to his earlier effort with another sublime finish.
Robling once again converted for Bedwas but with each side playing some Barbarian style rugby, the scoring was hardly about to end there.
Warren crossed for Llandovery's fifth try and when Knight finished in the right hand corner following another Robling penalty, a remarkable game was now tied at 41-41.
Garland's conversion of Knight's try put them back into a two point lead though Bedwas threw everything at them in the final stages.
Robling put a monster penalty effort wide and Hudd knocked on with the line gaping but Llandovery survived to set up a home play-off semi-final with Llanelli.