Liverpool hammered Spurs 6-3 in London on Sunday night.
Postecoglou later said, "Painful one for us, credit to Liverpool, they were too strong for us today and we were running on empty in terms of our energy levels which is quite understandable with the situation we're in.
"They're a good side and in a good moment. We racked up from Thursday night with the same team so that tells you a fair bit. It played a part but it doesn't take away they're a very good football team. It was a bridge too far.
"The lads tried as hard as they could but they met an opponent that was a little bit too sharp. I don't like losing. I said during the week we want to be an attacking team but we want to win.
"Not many sides have scored three against them. They're flying, really settled. Just look at the players they're bringing on, we're not at that level yet. I think I've explained clearly what happened today."