Llanelli or the Scarlets have played in every year of the Heineken Cup
The Scarlets say qualification for the 2010/11 Heineken Cup will be vital to "every aspect" of their business after their helping hand from the Blues.
The Llanelli-based region were destined for the Amlin Challenge Cup next season after finishing as the bottom Welsh region in the Magners League.
But the Blues' win over Toulon in the Amlin final secured a fourth Heineken spot for Wales at Gloucester's expense.
"It's so important to us as a region," said Scarlets team manager Garan Evans.
"You can look at every aspect, there will be more season ticket holders, it helps if you are looking to bring players in.
We got in through the back door when we would have liked to have done it ourselves
Scarlets team manager Garan Evans
"It's easier to sell the club when it's in the Heineken Cup.
"We got in through the back door when we would have liked to have done it ourselves.
"But all credit to the Blues for helping out the Scarlets."
Blues boss Dai Young was delighted his side could be of service to their west Wales rivals.
"I'm sure we've put a lot of smiles on a lot of Scarlets' fans' faces and I'm thrilled for that as well," said Young.
"They deserve to be in Europe - a lot of good things are happening down there so it will be great to have four Welsh regions in Europe next year."
The Scarlets become the 24th and final side to make next season's Heineken Cup.
If Toulon had beaten the Blues in Marseille, Gloucester would have claimed the last Heineken spot, but the Cherry and Whites now enter the 2009/10 Challenge Cup.
Munster, Toulouse, Leinster, Leicester Tigers, Biarritz Olympique and the Blues are the seeded teams and will be kept apart in the draw for the six groups.
Former Wales back Evans, who was watching the Blues-Toulon match in Marseille for BBC Radio Cymru, praised the Blues' gritty fight back for a 28-21 win.
"It was an excellent performance, the Blues were under a lot of pressure in the first half," said Evans.
"Once [Toulon's] Jonny Wilkinson went off the big ball carriers for the Blues came to the fore.
"They were by far the stronger team and deserved victory."