Albacete took the lead in the 42nd minute when defender Javi Villar headed Jose Lazo’s corner past Andriy Lunin.

Madrid responded promptly in first-half stoppage time through Franco Mastantuono.

But substitute Jefte Betancor scored twice – either side of Gonzalo Garcia’s equaliser – in the final eight minutes of the game to seal the Segunda side’s place in the quarter-finals of the competition with a first victory over the 15-time Champions League winners.

Arbeloa, who was named Real manager after Xabi Alonso’s departure on Monday, was without forwards Kylian Mbappe and Rodrygo and England midfielder Jude Bellingham at the Estadio Carlos Belmonte.

But the former Spain international was unable to arrest Real’s recent slump – just days after the Spanish Super Cup defeat by Barcelona.

Despite having nearly 80% possession and five shots in the first 42 minutes, the La Liga side found themselves behind when Villar rose highest to head home a corner.

Madrid restored parity within six minutes and went into the break level thanks to 18-year-old Mastantuono converting from close range after a mistake from goalkeeper Raul Lizoain.

There was little to separate the sides in the second half, which led to Arbeloa introducing four substitutes – including David Alaba, Eduardo Camavinga and Daniel Carvajal – as his side pushed for a winner.

But it was the changes from Arbeloa’s opposite number, Alberto Gonzalez, that proved decisive as Bentancor scored either side of Garcia’s effort to seal a historic victory for the home side.