The Catalan made nine changes to the side that drew 1-1 with Southampton on Sunday as he looked to keep things fresh ahead of the trip to West Brom on Saturday and the Champions League match with Barcelona three days later.
Garcia, 19, was superb in a deep-lying midfield role, using his exceptional range of passing to keep City’s play fluid - and Spanish right-back Maffeo gave a stellar display in difficult circumstances.
"Aleix was outstanding – Pablo Maffeo as well, fighting with [Marcus] Rashford and [Paul] Pogba,"
"We are a young team. Kelechi is 20,
The result saw City’s winless run stretch to six matches – the first time in Guardiola’s management career he’s gone so long without a victory – but he insisted he is pleased with his side’s performance.
"Yeah, it’s six games – not a good situation – but we are out of one competition, we have three still," he said. "We are going to see. I happy with the players and we are going to try in the future."
City saw plenty of the ball but struggled to turn possession into clear-cut chances, which Guardiola feels let his side down.
"At that level, you have to be precise," he said. "We had many opportunities to make the last pass but we didn’t finish and that’s why we didn’t win."
Guardiola also moved to allay fears that Vincent Kompany had suffered another injury.
The Belgian defender, 30, has struggled for fitness over the past two seasons – but he has started the last two matches and looks to be putting his injury concerns behind him.
He went off at half-time at Old Trafford, leading to speculation he had aggravated the groin problem sustained at Swansea last month that saw him miss three weeks.
But after the game Guardiola confirmed it was in fact Kompany himself who asked to be taken off.
"He told us he is tired and was not ready to play the second half," Guardiola said.
"The important thing is he is not injured - that is a good step."