But Commons said: “We have lads who have played in the Champions League, Europa League, international football.
“They came in needing goals and came out on the front foot whereas we were perhaps just trying to do enough to keep a clean sheet.”
Celtic had a goal disallowed in the first half after Nir Bitton was judged to have committed a foul and Commons believed that decision had a major bearing.
He said: “I think if we’d have come in 1-1 at half time then it puts a whole different complexion on the game.
“Once they scored we began to take chances. Second-half, they sat in and defended their own 18-yard line and tried to hit us on the counter-attack.”
Scott Brown admitted he was “ashamed” of the performance, but Commons said: “That’s Scott’s opinion.
“I’m bitterly disappointed and angry. I feel like it’s a good opportunity missed.
“At this level, if you’re not quite at the races, you get punished no matter what team you play.”