Despite the loss of Rogers in the summer, Scarlets showed they still possess plenty of threat in the back three.
Staring down the barrel of another loss when trailing Benetton 21-7 at half-time, Blair Murray, Ellis Mee and Macs Page helped swing the game before Costellow’s late kick.
Full-back Murray was player of the match after being a constant menace with ball in hand and coming up with a crucial interception.
That try was followed by a stunning finish by Mee after a break by Page, who continued his strong start to the season.
Mee scored his second with fast footwork and, after starting against Argentina and South Africa in July, has the nuts and bolts to remain in Tandy’s Wales line-up.
“We want to create an environment where we get these guys on the ball,” said Scarlets director of rugby Nigel Davies.
“Because of the errors in our game, we couldn’t do that in the first half, but in the second half we did.
“Our highlight reel is quite spectacular after three games, but we need to be more consistent in how we deliver that.”
With Bristol’s Louis Rees-Zammit having returned to the wing and Josh Adams nearing a return from injury for Cardiff, wide slots are being taken up for the Wales squad.
But if Tandy wants stardust then uncapped Page, an unused member of the touring party to Japan in 2025, could be a wildcard option.
“He has a low centre of gravity, is very quick and has a great rugby brain,” said Davies.
“He is similar to someone like Shane Williams – he is all X-factor and is probably one of the first names on our team sheet.”
