The omission of Jack Butland in goal after what head coach Barry Ferguson described as "one of the toughest things I've had to do", with Kelly in from the start, was such a big call on such a massive occasion. For him to emerge as the hero was full justification.
Starting Kelly and 18-year-old midfielder Bailey Rice among six changes from the defeat by Hibernian last weekend showed Ferguson was true to his word to be decisive following another domestic downfall.
Athletic Club clearly bring threat and Maroan Sannadi had already shown that before Rangers' suffered that disastrous early setback.
Propper's challenge on Williams was rash and, as last man, it is hard to argue his overturned yellow card did not merit a red.
It looked like Rangers' troubles were far from over, but yet again they mustered another memorable European performance to stay in the tie, with Ferguson saying the "few home truths" he had with his players had "sunk in".
Sannadi was a constant threat until substituted. Early in the second half, he went down under Leon Balogun's challenge, was booked but seemed to have a case for a penalty. It was a big let-off.
As it was moments later when Sannadi stretched to reach Inaki Williams' sharp cross and, with the goal gaping, and Kelly completely exposed, the striker blazed just wide.
The visitors repeatedly pushed and thought they had the opener when Berenguer fired home from close range.
Confusion reigned all around Ibrox as VAR intervened, offside was given to rule out the strike, but then a twist as Dujon Sterling was penalised for the slightest of handballs in the build-up.
It was to be Kelly's big moment. He stuck up a leg as he dived to his right and clipped the ball over the bar to Berenguer's dismay.
Big ties demand big moments and they do not come much bigger as Rangers survived mounting pressure to earn a memorable outcome.
Martin Dowden
