Swansea City were worthy 3-2 winners on Wednesday night, with two goals in injury-time stunning their Premier League opponents.
Postecoglou said afterwards: “No, not really. A lot of those changes we had to make because some guys still aren’t in the physical condition to see out the game. You could tell they were tiring."
Igor Jesus scored both of Forest's goals and Postecoglou continued: “Even with the guys who came on, it just needed some calmer heads and being a bit more clinical in our actions - both in taking chances but also in the way we set up. We just allowed the opposition to get into the game.
“You can look at some positive performances. But ultimately the overriding factor is we are out of a cup competition that really we should have progressed in. That opportunity, we shouldn’t have lost.
“We can look at the individuals within that, and there were some promising performances. It was important that some of the guys played - you could see they needed a game. But all that fades away when you realise we missed a great opportunity to progress.”