Rosberg, who had led the race at Monza from the start, was coming under increasing pressure from a recovering Hamilton following the duo's pit stops when he out-braked himself at the first chicane, allowing the Briton to slip into a lead he would not relinquish.
"Lewis was quick, coming from behind," Rosberg explained. "I needed to up my pace and then as a result just went into the mistake. That was very bad and lost me the lead in the end.
"Monza is one of the most difficult tracks for braking because of the low downforce and the highest speeds of the year. That isn't an excuse, that's just the way it is. Unfortunately I got it wrong."
Though Hamilton was able to cut Rosberg's championship lead down from 29 to 22 points, the German said he was not overly distraught at finishing second.
"It's not a disaster, that is a fact. I need to quickly look at the reality: second place, it's okay," he said.
"There's a lot worse than that. I lost seven points to Lewis, so, you know, that's the frame of mind that I'm trying to take.
"I am very, very disappointed inside. But there's no point now to go hanging my mouth down and things like that. It's still a one-two for the team and that's a great day."
Hamilton meanwhile said his mid-race charge was influenced by his belief that he would not have been able to attack Rosberg once tyre grip started to fade.
"The car felt good and it was the closest I had been at that point," he said of his charge.
"During the previous stint I knew when I was behind others - when I was behind Nico - when I got closer to him on the older tyres it was very hard to stay with him," he said.
"The engineer said that I should stay back, but knowing from experience - particularly this year - I knew that that wasn't the way forward, so I chose another route."