The 19-year-old, a boyhood City fan, is showing both versatility and composure beyond his years.
O'Reilly, whose primary position is attacking midfield, has also featured at left-back when needed - a decision Guardiola praised, highlighting the youngster's "versatility and selflessness."
His adaptability has proven vital in a season where little else has gone right for the defending champions.
"Physicality, presence, attacking midfielder, (he is) composed with the ball, (I am) surprised how defensively attentive he is, (he) has pace.
"(O'Reilly) gives us an extra player on set pieces that helps because we're weak in that position, generosity to play a position he's not used to and giving everything.
"In the back-four now, we're stable - pace with Josko (Gvardiol), Mateus (Nunes) and Nico (O'Reilly) because they're so fast and the intelligence, leadership, unbelievable leadership from Ruben (Dias)."
After winning the Premier League for three consecutive seasons (2021–2024), City surrendered their crown to Arne Slot's Liverpool and failed to mount a serious challenge this time around.
European disappointment followed, as City were eliminated from the UEFA Champions League in the Round of 16 by Carlo Ancelotti's Real Madrid, suffering a 6-2 defeat on aggregate.
With the league title out of reach and their European journey cut short, the FA Cup remains City's only realistic chance of silverware.
O'Reilly has played a key role in their run to the final, contributing match-winning performances.
Bayern Munich have reportedly taken a significant step toward securing Bayer Leverkusen's star midfielder Florian Wirtz, with reports indicating that the two parties are nearing a verbal agreement on personal terms.
Manchester City secured their place in a 14th FA Cup final with a commanding 2-0 win over Nottingham Forest in a one-sided semi-final at Wembley.
Manchester City have reportedly launched an aggressive push to sign Bayer Leverkusen's Florian Wirtz, targeting the 21-year-old as the ideal successor to their departing icon Kevin De Bruyne, according to multiple sources.
Manchester City took a significant step toward securing Champions League qualification with a dramatic 2-1 victory over Aston Villa at the Etihad Stadium on Tuesday evening, courtesy of a stoppage-time winner from Matheus Nunes.
