O'Riley, who's been a revelation since joining the first team, scored his fourth goal in 14 games, this time as a left-back.
City's manager was effusive in his praise, admitting he's 'so grateful' to have the youngster.
“He's an attacking midfielder, and when you play as a left-back, you can arrive there,” Guardiola said.
“He always is there. Look at Plymouth and Bournemouth. When you play full back, you score. Look at Josko before, now him.
“We are so grateful because he’s not a left-back. They have so many tall, strong players. When the take is good and you are tall, you have a chance. They hit the post and then Stefan makes a save.
“They make a good 10 minutes in the second half, but then we work hard to find the goal.”