Olayinka, 18, struck in the 3-0 win.
He told arsenal.com: "I just picked the ball up on the edge of the area and when I looked up, I saw the keeper on the other side. I took a shot, made sure it was on target, and luckily it went in.
"I was actually on the floor when I kicked it, so when I looked up, it was just in time to see it hit the net. It's a great feeling. I'm just happy I got the goal really."
Olayinka added: "I've been here for 12 years now, so to finally score for the first team is a great feeling. I'm sure everyone at home is happy and hopefully there are many more to come."
Fantastic goal from Olayinka pic.twitter.com/ISEehe9ogK— The Centre Of The Arsenal (@ArsenalBeezer) July 16, 2019