Moses climbed off the bench in the 80th minute and snatched victory in the last action of the match after Willian had cancelled out strikes from Fernando Torres and Oscar.
The injury-time winner lifted the defending champions level with the Ukrainian visitors at the top of Group E.
"It was crucial for us to win this home game," said Di Matteo. "It was obviously going to be a tough game that would be decided by the little details.
"They are a very good side and they showed tonight how good they are. It will probably go down to the last game and probably the last kick.
"We knew the kind of pressure we were under and it was must-win for us. We didn't want to expose ourselves too much. We knew we could have scored a goal with the last kick and that is what happened.
"We knew we needed to score a goal probably from a set play. It was good Victor got on the end of it.
"I think in the first half we put them under pressure and we managed go ahead with good pressure.
"Then in the second half we tried but they were a good side. We probably didn't have many chances as normal, but sometimes need a goal like that."