O'Brien (28), playing for the Albion Devils team in a fourth-grade match, knocked up 221 for his side in a big win over a Green Island side.
O'Brien smacked 22 fours and 14 sixes in his hefty knock, off 100 balls.
He was using a new Kookaburra Kahuna Players bat, and it appears to have a hefty sweet spot.
"That was its christening, and it certainly was pretty handy. I was seeing it pretty well and managed to hit them straight and long," he said.
"I thought I had got to 50 when I did and then the 100 came along pretty quickly. From there the hits were pretty much coming out of the middle. The 150 and then 200 came along pretty quickly.
"It was all boundaries really. There weren't many ones or twos."
"When I was getting close to the 200 even the opposition was egging me on. They said if I made 200 it would be a double shout, and I'd have to shout them."
He was out off the third-to-last ball of the 40-over innings, yorking himself as he looked to make more runs.
He only went to the crease in the 12th over, and admitted he was helped by the smaller boundaries at the Sunnyvale ground.
O'Brien was dropped four times in his innings, although they were all tough chances.
Not surprisingly it was the highest score he had made, having previously notched up 178 when he played cricket in Auckland.
He played premier grade cricket for Pakarunga but had only played on and off since he moved south four years ago.
The team piled up 398 for the loss of just three wickets in its 40 overs and Green Island in reply could only muster 150, giving the Albion side a 248-run win.
The team sits second in the fourth grade table, behind another Albion team.
