Real Madrid were knocked out of the Copa del Rey by second division Albacete in Alvaro Arbeloa's first game in charge.
The former Liverpool and Real Madrid defender rested Kylian Mbappe, Rodrygo, Thibaut Courtois and Jude Bellingham before Saturday's La Liga game against Levante.
However, Arbeloa defended his decision to rest the quartet and select academy players Jorge Cestero and David Jimenez, as he insisted he "brought a team capable of winning".
"If anyone is responsible and to blame for this outcome, it's clearly me - the one who made the decisions regarding the line-up, how we wanted to play, the substitutions," said Arbeloa.
"I'm not afraid of failure. I understand anyone who wants to describe this defeat as a failure. Failure is part of the road to success.
"It will make me better, and it will make us all better. I've endured defeats harder than this one. We'll prepare for the next match with maximum dedication."
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 was named Real Madrid manager after Xabi Alonso departed the club by mutual consent on Monday.
But the former Spain international was unable to arrest Real's recent slump - just days after the Spanish Super Cup defeat by Barcelona.
Regarding to questions on player's status and Vinicius' downplay, Arbeloa was still confident and look up on the future:"Losing is never a relief. That wasn’t our goal here. We have a lot of room to improve physically. That’s what Antonio (Pintus) is here for, to give us that extra edge. It’s necessary.”“I saw players who wanted to win. I can’t reproach them. How they received me yesterday, the attitude they showed. We all know the expectations that come with this badge. Everyone goes to bed hurt tonight, but tomorrow we get up and work again.”
On Vinicius, Arbeloa expressed his positive feedback to the player's performance:"It was positive to see, after everything he’s done, especially following a long trip, that he wanted to play every minute. That’s the Vini I want to see, the one who takes responsibility. He’ll have brighter days and tougher ones. But if Madrid wants to win, we need his best version"
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.