The young midfielder played the full 90 minutes and was one of six Academy graduates to give a good account of themselves in a tight defeat in north London.
Spurs got out of the blocks quickly, scoring through Timo Werner and Pape Matar Sarr in the first 25 minutes before Matheus Nunes pulled one back on the stroke of half-time.
Spurs 2-1 City | Match report
City dominated the ball for the second period against a more experienced Spurs team and could have levelled the scores on several occasions, with O’Reilly himself seeing a shot blocked on the line.
“It’s never nice losing,” he said.
“I thought we played well and for the majority of the game we were the better team in my opinion for the majority of the game.
“We were getting chance after chance and couldn’t take it but that’s for us to go back to the training pitch and next time hopefully it’ll go in.
“It was a good block so fair play to him and then I had a header at the end but I mistimed my jump.”
The 19-year-old, who has now played four times for Guardiola’s team, was keen to congratulate his team-mate Jahmai Simpson-Pusey on his senior debut.
Simpson-Pusey was a second half substitute and looked extremely comfortable slotting into the defence.
“He’s such a composed player on the ball and a solid defender. I’m really happy for him as well because he’s one of my close friends,” said O’Reilly.