The Bhoys dominated large portions of the San Siro encounter but came up short as a deflected shot from Cristian Zapata in the 82nd minute and a close range finish from Sulley Muntari four minutes later ruined their night.
It was a solid display from Celtic, bar the late goals, but Commons says near enough is no longer good enough for the Scottish champions.
"We're disappointed not to get at least a point," he said.
"Milan had phases in the game but you need to take your chances and we were not as ruthless as we needed to be.
"The longer the game went on, you just knew they might get a chance and nick it.
"The gaffer said there are not many teams who come here and play as well as we did yet not come away with anything.
"The scoreline flatters them but you have to make your own luck."
He added: "Looking at how we played, you would have to say we'll look back at this as a chance missed.
"Milan wasted a lot of ball and I don't think our back four and keeper had that much to do, given we were in the San Siro.
"It's a tough one. You go to the San Siro and no one gives you a chance of getting a result. They have you beat before you get your kit on.
"So we have to look for the positives and we'll go into the home game against them feeling positive of getting a result."