Scarlets captain Ken Owens says qualifying for next season's European Champions Cup "means everything".
The Welsh region came from behind to beat Treviso away 17-13.
Victory means the Llanelli-based side secured the last automatic qualifying spot on the final weekend of the Pro12 regular season.
"We've had an indifferent season and it means everything to this region to be in Europe and I'm just glad we've done it," said the Wales hooker.
Scarlets have never failed to qualify for European club rugby's top-tier competition.
They needed just a draw in Italy and Owens admitted he felt the pressure during the Pro12 run-in.
"It's been weighing on my mind the last couple of weeks," Owens said.
"I didn't want to be the first captain not to make it."
Treviso also qualify for the competition as they finished as Italy's top side in the Pro12 thanks to Zebre's 29-5 defeat against Cardiff Blues.
Davide Giazzon and Jayden Hayward's tries helped Treviso into a 13-3 half-time lead,
But Scarlets fought back thanks to tries from Liam Williams and Steffan Evans, with Rhys Priestland kicking seven points in his final Scarlets game before joining Bath.
"Treviso are no mugs. They pushed Leinster all the way in Dublin last week," said Owens.
"They were fighting for their lives for a European spot as well and we knew it was going to be tough out here with the heat and the conditions.
"We just has to cut out our errors. We managed to do that to some extent at times in the second half.
"It wasn't pretty at times but we got the result."