Celebrating his European debut for the club, the 29-year-old repaid the faith shown in him from Barry Ferguson by denying Alex Berenguer from the penalty spot deep into the second half to ensure the tie hangs very much in the balance heading into the return leg in Bilbao next week.

It was a performance full of grit and determination from the Light Blues, who ended the match with nine men and were forced to play 80 minutes, plus a heavy dose of additional time, with a man disadvantage following the dismissal of Robin Propper.

Ferguson named six changes to his side which tasted defeat at home to Hibernian at the weekend, headlined by the introduction of Kelly between the posts in place of Jack Butland and 18-year-old Bailey Rice in midfield.

So often in Europe it has been Vaclav Cerny who has delivered the goods for Rangers, and it was little surprise when the Czech winger caused panic among the Athletic ranks inside four minutes when he shimmied inside and unleashed an effort which flashed wide of the goal.

However, any early Gers momentum was dampened just six minutes later when referee Istvan Kovacs of Romania went to his pocket and sent Propper for an early shower.

Indeed, there didn’t appear to be anything malicious in the Dutchman’s challenge on Inaki Williams on the edge of the penalty area, but the on-pitch referee was encouraged to take a trip to the pitchside monitor where it was deemed that Propper’s tackle on the Ghanian was denying a clear goalscoring opportunity.

Immediately, Ferguson reshuffled his pack and brought captain James Tavernier into his conventional full-back role.

Ibrox was sprung into a defiant noise as it was the hosts who fashioned the first opportunity following the dismissal of Propper; Cyriel Dessers swivelling on the edge of the danger area after Athletic had failed to deal with an in-swinging free-kick delivery from Cerny.

Down the opposite end and the away side were spelling out their danger in block capitals through the dangerous Inaki Williams on the right-hand side. The Ghanian was denied twice in quick succession, the second of which arriving from a delicious stood-up delivery from Inigo Lekue.

Athletic had begun to settle into a rhythm in possession as the first half ticked towards its conclusion, although Kelly had been a relative spectator between the sticks despite the man disadvantage.

But when he was called into action five minutes before the interval he was alert to a Maroan Sannadi effort before plucking a dangerous header from Oihan Sancet out of the air at full stretch from the subsequent corner.

Nico Williams then blazed wildly off target after being teed up by Mikel Jaureguizar, before the Athletic wide man turned creator on the stroke of the interval and could only drop to the turf in frustration when his brother, Inaki, and Sancet were unable to fashion an attempt between them.

Opportunities were, naturally, at a premium for the hosts, which magnified Dessers’ chance in first-half stoppage time when the Nigerian met Cerny’s deep free-kick unmarked but nodded wide of the target.

Athletic had really failed to make their man advantage tell in the first half and it was little surprise to anyone inside Ibrox that the visitors sprung out the traps quickly in the second period.

The Light Blues were grateful for a heroic last-ditch block from Dujon Sterling as Sannadi looked to pull the trigger, before Ernesto Valverde’s side came within a whisker of breaking the deadlock moments later.

It was Oscar de Marcos – retiring at the conclusion of this season – who was released in an advanced position on the right-hand side, fizzing a dangerous delivery across the face of goal towards Sannadi who diverted his first-time effort wide.

Chaos ensured with ten minutes remaining when Athletic had the ball in the net through Berenguer, himself introduced just moments earlier.

A searching pass over the Gers defence was met by the substitute who, after Gorka Guruzeta was denied by a fantastic Kelly stop, smashed home the rebound to break the deadlock.

However, a lengthy VAR check encompassing a handball check against the goalscorer, an offside, and a potential penalty review, it was adjudged that Sterling had handled the ball and the Spanish outfit would have the chance from 12 yards to deal a serious blow to the home side.

In keeping with the theme of the evening, Kelly rose to the challenge and denied Berenguer with his feet from the penalty spot; the Athletic substitute left to look sheepish by his decision to go down the middle of the goal.

It quelled the celebrations in the corner packed out in red and white Athletic attire, who will be very much wary of Rangers’ never-say-die spirit in this competition when the Gers descend on northern Spain in seven days’ time.

RANGERS: Kelly, Tavernier, Sterling, Propper, Balogun, Ridvan (Jefte, 66), Raskin, Rice (Barron, 66), Hagi (Bajrami, 90), Cerny (McCausland, 90), Dessers (Igamane, 83)

Subs not used: Butland, McGuire, Nsiala, Curtis, McCallion, Danilo

ATHLETIC CLUB: Agirrezabala, Vivian, Alvarez, Sancet (Berenguer, 73), I. Williams, N. Williams, Lekue, Ruiz De Galarreta (Prados, 60), de Marcos (Gorosabel, 90), Sannadi (Guruzeta, 60), Jaureguizar

Subs not used: Simon, Paredes, Vesga, Djalo, Nunez, Gomez, Canales, Boiro

REFEREE: Istvan Kovacs (ROU)