The tie finished 1-1, with Dejan Kulusevski canceling out Rangers' opener struck by Hamza Igamane.
Postecoglou said afterwards: "A tough game as expected, obviously with the atmosphere in the stadium. I thought the first half was pretty tight with no clear-cut for either side.
"When they score straight after half-time the energy levels obviously go up and it's going to be a tough one to claw back, but I thought we worked our way back in well.
"I thought the substitutes made a difference and we scored a good goal, had other good moments and a great save by Fraser (Forster) at the end.
"In the context of where we are in Europe, an important point."
On Werner, who was taken off at half-time, Postecoglou said the Germany striker "wasn't playing anywhere near the level he should".
And on Rangers, Postecoglou added: "They're always difficult to play against here at Ibrox, especially on European nights.
"The nature of the contest, the atmosphere, not many teams come here and win so you kind of expect it to be a tough game.
"We weren’t anywhere near our best which I think is fair to say and at the same time, we’re in a period of games where we’re grinding through at the moment.
"Obviously with a fairly depleted squad. So, in the context of that, in the end, I think it was a good outcome for us."