John Hartson opened the scoring for Celtic after 67 minutes, but Celtic threw away the lead and eventually lost the game to a Shota Arveladze goal in extra-time.
The defeat marked the end of Celtic's winning run against Rangers - it was our first defeat in the last eight games against them.
But O'Neill claims he knew the winning streak had to end sometime. He said, "I thought we were going to win it and I thought we were reasonably comfortable at the time they got the equaliser.
"Obviously I'm disappointed but it is not the end of the world. I have no qualms about it. I have been a fair length of time in this life and yes, all good things do come to an end, there is no doubt about it."