A place in next season’s Champions Cup is up for grabs at Liberty Stadium on Saturday when Welsh regions the Ospreys and Scarlets face-off.
Ospreys finished with a higher number of points than Scarlets at the end of the season and thus have home field advantage for this fixture.
In team news, fly-half Sam Davies will play his 150th game for the hosts after being named as a starter alongside Aled Davies.
Justin Tipuric once again captains the side from the back-row and is joined in the pack by the likes of Alun Wyn Jones and Scott Baldwin.
“It’s a one-off game and the prize is huge,” said head coach Allen Clarke ahead of the crucial match.
“Our games with the Scarlets in recent seasons have been tight, one score contests, and you would expect this to be similar.
“We know what we have to do, we know what we are about, and we have to focus on what we do well, what has got us into this position over the last two months.
“There’s a respectful excitement about us and we want to represent our region, in front of our own supporters, having left everything out on the pitch.”
Meanwhile, Scarlets lock Jake Ball will make his return from injury in this Champions Cup play-off.
Ball injured a foot during the latter stages of the Six Nations campaign, but has recovered for the crucial derby clash that will decide which Welsh side competes in the top tier of European rugby next season.
The second-row is one of four personnel changes, all of them up front, to the side that took the field in the Scarlets’ last outing against the Dragons on Judgement Day.
Injuries to Rob Evans and Wyn Jones sees Phil Price start at loosehead, although Jones does feature on the bench.
On the other side of the scrum, Samson Lee is ruled out because of concussion so Werner Kruger steps in at tighthead prop.
Ball partners Steve Cummins in the second-row, while in the back-row Blade Thomson makes his first start since November and wears the eight jersey. Josh Macleod switches to blindside with Will Boyde starting at openside.
Wales internationals Aaron Shingler and James Davies have failed to recover from injury, but hooker Ryan Elias returns from a shoulder issue to take his place on the bench.
Scarlets head coach Wayne Pivac said: “We have a proud history in the top echelon of European rugby and clearly that is where the club would like to be again.
“We have prepared well and we have all talked about the importance of the game.
“Ordinarily, the Ospreys is one of the big fixtures of the season so to have this added game, there is a lot of motivation for both sides.”
Ospreys: 15 Dan Evans, 14 George North, 13 Cory Allen, 12 Owen Watkin, 11 Keelan Giles, 10 Sam Davies, 9 Aled Davies, 8 Dan Lydiate, 7 Justin Tipuric (c), 6 Olly Cracknell, 5 Alun Wyn Jones, 4 Adam Beard, 3 Tom Botha, 2 Scott Baldwin, 1 Nicky Smith Replacements: 16 Sam Parry, 17 Rhodri Jones, 18 Ma’afu Fia, 19 Bradley Davies, 20 Sam Cross, 21 Matthew Aubrey, 22 Luke Price, 23 Hanno Dirksen
Scarlets: 15 Leigh Halfpenny, 14 Johnny McNicholl, 13 Jonathan Davies, 12 Hadleigh Parkes, 11 Ioan Nicholas, 10 Dan Jones, 9 Gareth Davies, 8 Blade Thomson, 7 Will Boyde, 6 Josh Macleod, 5 Steve Cummins, 4 Jake Ball, 3 Werner Kruger, 2 Ken Owens (c), 1 Phil Price Replacements: 16 Ryan Elias, 17 Wyn Jones, 18 Simon Gardiner, 19 David Bulbring, 20 Uzair Cassiem, 21 Kieran Hardy, 22 Rhys Patchell, 23 Paul Asquith
Date: Saturday, May 18 Venue: Liberty Stadium Kick-off: 19:45 BST (18:45 GMT) Referee: Ben Whitehouse (Wales) Assistant referees: Nigel Owens (Wales), Dan Jones (Wales) Television match official: Ian Davies (Wales)