The Hoops hit the lead in the 19th minute when Kris Commson converted from the penalty spot but Locke could not quite work out why referee Willie Collum made the call for handball against Jamie Hamill.
"Unfortunately for us, there was only one man in the stadium who thought it was a penalty and he was the most important one," said Locke who saw his side level through Jason Holt before Celtic struck twice in the final 25 minutes.
"I think you can see with the reaction of players and not one Celtic player appealed for a penalty and no one in the Celtic dug-out appealed for a penalty but, unfortunately for us, the referee gives it so there's not a lot you can do about it.
"There's no point (talking to him) because at the end of the day, the decision is not going to get changed.
"The problem is you don't get an explanation from anyone and if Hamill's hand was in an unnatural position that puzzles me because his hands weren't in an unnatural position from where I was.
"It is difficult enough to beat Celtic but when you get a decision like that it makes it tougher.
"But there is no point in moaning about it, there was plenty time to get back into the game.
"I am not going to use that as an excuse and there is a lot more positives than negatives I can take out of the game."