The West Wallians are winless in Europe so far this season but still harbour hopes of knockout rugby.
Friday’s fixture between Pau and Bulls will dictate whether they can sneak into the last-16 or whether they are playing for a spot in the Challenge Cup.
Following the return of Davies to lead the Llanelli-based outfit, the former head coach has made minimal changes to his first selection.
Costelow’s return will be welcomed having not featured for the Scarlets since the round two tie in Bordeaux in December because of an ankle injury picked up in training.
In the back three, Jac Davies, who featured in the opening rounds against Bristol Bears and Bordeaux-Begles gets the nod at full-back. Tom Rogers is ruled out with a groin injury so Blair Murray switches to the left wing and Ellis Mee moves across to the right.
With Costelow back in the number ten jersey, Joe Hawkins moves to inside centre and Eddie James to outside in place of the injured Joe Roberts, who picked up an ankle issue in the home defeat to Pau last weekend.
Archie Hughes continues at scrum-half following an impressive try-scoring showing against the French side.
In the pack, the front row of Kemsley Mathias, Ryan Elias and Henry Thomas remains the same.
Max Douglas returns from suspension to partner Jake Ball in the second row, while it’s same again for the back row of Taine Plumtree, Fletcher Anderson and skipper Josh Macleod.
Tomi Lewis, Macs Page and Gareth Davies are named as the backline cover on the bench, while flanker Jarrod Taylor also comes into the matchday 23.
Speaking ahead of the match Interim Director of Rugby Nigel Davies said:
“We’ve simplified things, and we’ve taken noise away. I’ve been delighted with the way that the players have trained and bought into it.
“There’s a genuine excitement around the group to take on this huge opportunity. Belief is everything and we’ve got the talent
“We’ve got to play to what is a very basic game plan that is based on a lot of the old values of the Scarlets, but in the context of a new era.
“I’m excited by the group. We have got some tremendous coaches and players and have a great opportunity to go up against one of the best teams in Europe and show what we’re about.
“Not many people give us much of a chance, and understandably. They’re a fantastic team, and at this moment in time, we’ve not been on the right end of results.
“They are the hot favourites and we have to make sure we are in the right place to perform.”
Scarlets XV to face Northampton Saints:
15 Jac Davies, 14 Ellis Mee, 13 Eddie James, 12 Joe Hawkins, 11 Blair Murray, 10 Sam Costelow, 9 Archie Hughes, 1 Kemsley Mathias, 2 Ryan Elias, 3 Henry Thomas, 4 Max Douglas, 5 Jake Ball, 6 Taine Plumtree, 7 Josh Macleod (captain), 8 Fletcher Anderson.
Replacements:
16 Marnus van der Merwe, 17 Alec Hepburn, 18 Harri O’Connor, 19 Jarrod Taylor, 20 Dan Davis, 21 Gareth Davies, 22 Macs Page, 23 Tomi Lewis.
[Lead image: Scarlets Rugby]
