Celtic scored an early goal when Reo Hatate converted a penalty in the 14th minute, but they were in some jeopardy when Joe Hart was sent off in the 28th minute.
The Bhoys protected their lead until half-time and O’Riley doubled their lead just three minutes into the second half to give Celtic some breathing space, while Daizen Maeda sealed the win with a third goal in stoppage time.
O’Riley stressed that Celtic kept calm even after going down to ten men and trusted their ability on the ball to control the pace of the game.
He conceded that it was a good test and the midfielder was happy that the team managed to keep a clean sheet despite the jeopardy of playing with ten men for more than an hour of the game.
The Bhoy said on Celtic TV: “It’s about staying calm right in your head when it gets to that point because we know we’ve got the quality to keep playing.
“As long as you are comfortable on the ball, you need to take in those situations when you are a man behind, as long as you are comfortable in those situations, it’s not a problem because you can protect it and someone will be free eventually.
“Yes, definitely it was a good test for us in terms of that confidence that you can keep clean sheets even if things are going against you.
“Even on Tuesday night at Feyenoord, we had nine men and the boys stuck at it for the whole game.”
Celtic have a week to prepare for their next game when they travel to Motherwell.