The majority of players of are used to doing battle with each other week in, week out in the Guinness PRO14, with the Irish provinces edging the battle for titles in recent years, winning four of the last six Championships.
Scarlets sensationally stormed to the 2017 title, followed by Leinster in 2018, and the two clubs met head on in the second round of last season’s Guinness PRO14.
The line-ups included many of those who could feature in the World Cup warm-up on Saturday. For Scarlets the likes of Leigh Halfpenny, Hadleigh Parkes and Gareth Davies lined up, while Leinster were led by Jordan Larmour, Robbie Henshaw and Tadhg Furlong.
What transpired at Parc y Scarlets last September turned out to be one of the games of the season, as the West Walians survived a late scare to defeat the defending champions 23-21.
Early on, James Davies, Kieron Fonotia and Parkes combined to send Johnny McNicholl away, but the Kiwi was halted five metres out before successive penalties saw Leinster flanker Josh Murphy sin-binned.
Scarlets continued to threaten and the Leinster defensive wall was finally breached when Wales hooker Ken Owens crashed over, with Halfpenny converting for a 7-0 lead.
Leinster’s pack retaliated and rumbled 20 metres from a line-out – with the Scarlets defence on its heels Sean Cronin burst down the middle and Rory O’Loughlin found Fergus McFadden for the score.
Ross Byrne converted to level the scores before a blindside passing move saw Jamison Gibson-Park find the fly-half to put James Lowe over in the corner.
Byrne added the conversion from out wide as Leinster surged into a 14-10 lead at the break, but Scarlets edged back ahead with two penalties from the boot of Halfpenny.
A handling error from Leinster inside their own 22 then set up the hosts for their third try, after Parkes sliced through the defences and offloaded to Davies on the outside.
Halfpenny added the extras to give the home side a nine-point lead heading into the final ten minutes, but Leinster showed their never-say-die attitude to close the gap again.
A try from Rhys Ruddock, who burrowed over from close range, and another Byrne conversion made it a two-point game at 23-21 with just minutes remaining.
But Scarlets held on during an exhilarating finale – fans of the game will hope for similar excitement this weekend.