City won 3-0 on Sunday night, with O'Reilly keeping Mohamed Salah quiet on the night.
Guardiola enthused afterwards: “He has been a nightmare, Salah, for many years. He’s top.
“I said to Nico you have to be aggressive. He had help from central defender and midfielders every time Mo had the ball.
“Jeremy (Doku), Bernardo (Silva), Phil (Foden) were all there. It was incredible teamwork, but Nico made a step up because at the end you have to prove yourself against the best wingers.
“There is no better example to do it when you play against Salah, he did really good. He’s with the national team because Thomas (Tuchel) is smart enough to see how he’s been playing.
“He had many good attributes but this intensity in duels he didn’t have in the Academy because he was an eight or a 10 in midfield. I’m so pleased with the way he performed.”