"The people up front were not as brilliant as normal, but all the other guys were so good, especially Nico and Eric," he said. "Eric Garcia, at 17 years old, made an incredible performance."
It was indeed not City's most fluid night at the King Power Stadium, their makeshift team looking laboured for large parts, especially in the second half, and it took three penalty shoot-out saves from 20-year-old goalkeeper Aro Muric to send the Blues into the semi-final.
Muric revelled in the chants of the travelling support following his heroics, his team-mates pushing him out in front of the celebratory huddle to enjoy the moment, and the giant Kosovo international will remember a landmark night in his career.
But so too will Garcia, who on this evidence is a centre-back with incredible promise. City signed him from Barcelona as a 16-year-old in the summer of 2016, a move that prompted Barca fans and journalists to bemoan the loss of one of the club's highest-rated talents.
He had been at Barca since he was seven years old, captaining every youth team he had been in, even when playing in older age groups, and those who know the youngster all come back to one word: maturity.
“Eric Garcia is 17 or 18 and played like he is 24 or 25,” Guardiola said during the summer, when Garcia first showcased his talents in the City first team.
And that was the case again on Tuesday night in the East Midlands. Garcia, at such a young age, spent the night gesticulating at his considerably more senior team-mates, telling them where they should be stood, where they should be passing.
"He has a lot of personality," Guardiola said when asked about Garcia. "In pre-season in the States he was incredible, commanding the line against Bayern Munich and Liverpool.
"He's a guy that has a lot of sense of the position. He's so smart, he's not the strongest in the air or the fastest one but few times the opposition win one position, he's able to guide the line and has a lot of personality to play."
That maturity is evident off the pitch, too. In a post-match interview - delivered in perfect English - Garcia spoke as if it's perfectly normal for a teenage footballer to step into one of the best teams in Europe and start telling senior internationals what to do.
"I always say when we are on the pitch we are all the same team," he said. "I think if we speak to each other it is better for the team, because you try to help your team-mates and at the end that’s the most important thing. Obviously with the age there’s a lot of difference but I just feel that I need to do it."
Guardiola, despite his Barca links, did not know much about Garcia before he moved to Manchester, but has been incredibly impressed by what he has seen since. That came across on Tuesday as he highlighted the youngster's other key attributes.
"He has good vision, a good pass. It's incredible, I'm very pleased," Guardiola added. "He didn't make one mistake and with the ball he played with huge personality. It's not easy with [Demarai] Gray, Kele [Iheanacho] and [James] Maddison.
"It's a big important event. I'm so delighted with his performance."
And Garcia, with his commitment to playing out from the back, is just as thrilled to be working with Guardiola.
"I think that he helps me a lot every day, every day is like if you go to school because you learn something different, so it’s good."
And he says that nights like these, his first competitive senior appearance for City, justified the decision to leave Barcelona.
"Yeah, yeah, yeah, I’m really proud of my decision," he said. "It’s difficult because you leave your friends, your family and your old team-mates, but at the end I need to think about my career and I’m really happy for this.
"I think it’s going in the right way, I’m playing with the U23s and I’m 17 years old so I’m really happy at the moment."