The fly-half struck the extras from the left touchline following Ryan Conbeer’s late try. Leigh Halfpenny, Costelow himself and Johnny Williams also crossed the whitewash in a thrilling contest under the lights.

Clermont played their part, battling for 55 minutes with 14 men after Irae Simone was given his marching orders following a high tackle on Halfpenny. Simone, Alvereti Raka (2) and Giorgi Beria notched for the defeated visitors.

WHAT A FINISH 😱@scarlets_rugby sneak into the semis late on, for the first time in their history 💪

Reaction?#ChallengeCupRugby pic.twitter.com/xZwRfdY91L

— EPCR Challenge Cup (@ChallengeCup_) April 7, 2023

Anthony Belleau earned the first opportunity of the contest as he connected with a penalty from the tee with three minutes played. Halfpenny responded three minutes later with a penalty of his own to level for Scarlets.

A sensational finish from full-back Halfpenny then brought the first try of the contest on seven minutes. The hosts swiftly moved the ball through the hands to the right flank where wing Steff Evans floated a kick over the Clermont defence and across the whitewash, Halfpenny dotting down with his fingertips.

A second followed seven minutes later – A fumble by Clermont scrum-half Baptise Jauneau gifted the ball to Scarlets who, through a combination of Williams, Evans and Costelow, grubber kicked the ball down the field before the latter picked up to score.

Midway through the half, Damian Penaud, who’d been quiet early on, kicked the ball down the right wing as the ball bounced awkwardly inside the Scarlets 22 before Simone had the awareness to gather and cross the whitewash.

Simone would go from hero to villain, however, as he was given his marching orders four minutes later. A shoulder to the head of Halfpenny had no mitigation in the eyes of the officials, earning the Clermont centre an early bath.

The man disadvantage seemed to spur on the visitors, who were also buoyed when Scarlets lock Vaea Fifita was sent to the sin bin for bringing down a maul illegally.

Jauneau was alert at the back of a scrum to find Belleau, who floated a beautiful cross-field kick into the path of wing Raka who scored in the corner. Belleau added the extras, then soon after added a penalty to put Clermont 18-15 ahead.

MAE'R SCARLETS YN Y ROWND GYNDERFYNOL! 🙌

Am sŵn ar Barc y Scarlets! 😍

32 🔴 v 🟡 30
📺 @S4C #SCAvASM | @scarlets_rugby pic.twitter.com/pBPCqHmPIC

— S4C Rygbi (@S4CRygbi) April 7, 2023

That lead lasted just two minutes as Alex Newsome gifted Williams the go-ahead try. The full-back’s errant pass was intercepted the Scarlets centre, who accelerated away from two defender to add the Welsh region’s third of the night moments before the interval

The visitors started the second half strongly and were encouraged when Scarlets scrum-half Gareth Davies was sent to the sin bin for tripping. Soon after, Raka notched his second try of the contest as Clermont swiftly moved the ball from left to right following a kick to the corner.

The visitors began to dominate the contest, running through the phases to slow the game down and take time off the clock. Their rolling maul then paid dividends as Beria powered over to open up an eight-point lead.

Costelow reduced arrears with a penalty as contest approached a nail-biting conclusion, Conbeer then powering over in the corner as Scarlets cranked up the pressure on the depleted French outfit.

That left a tricky kick for Costelow to add the crucial extras, but he dissected the uprights coolly with just three minutes left on the clock.