Brandon Thomas-Asante had Coventry ahead before Djed Spence on 88 minutes and Brennan Johnson in the 92nd minute earned Spurs the Cup win.
Asked about the performance, Postecoglou insisted: "Yeah, I don't know, flat performance is a bit harsh. I thought I was a typical cup game. I thought Coventry were really good. They put some real energy into the game, and we couldn't really get a grip on it. So we had to hang in there. We had to work really, really hard just to stay in the game and obviously going a goal behind makes it even more challenging.
"But like you said at the end there we showed some real spirit and character, which is probably what's been missing in the first four games. We've had the performance, but we haven't had that relentlessness to to get a result. You sense that in the last 10 minutes, we got real belief out of that, and hopefully that's a good sign moving forward."
On Tottenham's goalscorers, he said: "Yeah both were really good. They made an impact when they came on. Look, it was it wasn't an easy night for us, as I said, credit to Coventry. But, you know, a lot of guys getting first starts, but I really think there's some positives in there with Archie and Lucas and these guys getting some significant game time for us.
"And Djed, and as you said with Brennan, you know I spoke about it yesterday that he comes in, works hard at his game and when you're an attacking player, you're always kind of getting measured against certain things. I said, if he can get through this period and just be positive and and play like he can, he can be a significant contributor to us and credit to him. He got a good goal tonight."