Roma earned an impressive 2-2 draw in London on Thursday.
Postecoglou later said, "Yeah frustration with the way the game ended. Yeah we should have killed it off a lot earlier. We should have killed it off in the first half with the chances we had. At 2-1 you're always keeping the opposition in the game and they're throwing men forward, so disappointing we weren't able to see the game out. Ultimately we're still in a decent position.
"It is what it is. We've been in this situation for quite a while. We are fairly thin in terms of squad depth at the moment. We had four kids on the bench tonight so we couldn't even fill the quota. It is what it is, we've been dealing with this for quite a while and I still think we certainly had enough of the game and enough clear cut chances to win the game.
"I think tonight our football was still good but we just lacked a bit, that clinical edge to finish the game off. Overall this whole European competition, we've had some challenges within the first five games so we're in a strong position and that's the main thing."