Penrith Panthers coach Ivan Cleary has admitted he thought Sunday evening's grand final against the Brisbane Broncos was heading towards being a lost cause before a dramatic comeback in the final 20 minutes.

Nathan Cleary would ultimately spark the Panthers into action as they reversed a 16-point deficit over the final 18 minutes to win their third straight premiership.

The coach said post-game that while he was thinking the game was gone, there was enough time on the clock, and that his side would never stop fighting.

"A fairly big part of me was leaning that way [that we are gone]. One thing I've never doubted though is the ability of these boys to keep fighting. It's just one of those games where you get one back and things can change. There was still a long time to go and I think that was the important part," the coach said during his post-game press conference.

"If they had of jumped to 24-8 with 15 to go or something, I don't think we would have come back but it was just enough time to make them get nervous. Once they hit the front and we started coming back, they didn't play as much footy as they had been. It felt like they had been zinging it around all game with offloads and getting it wide, they are an absolute handful.

"But once we got some possession, we had a chance."

Clive Churchill medallist Nathan Cleary said it was all about attempting to get back into the arm wrestle before they could think about a comeback.

2023 NRL Grand Final - Panthers v Broncos

"I wasn't thinking that far ahead, but we were just trying to stop the flood at the time. We just wanted to get back into that arm wrestle, once we got one, that turned into two, then before I knew it I looked up at the clock and there was ten minutes to go, and we were down by four. That's when belief started to set in," the halfback said.

The comeback came after Ezra Mam put on a hat-trick in quick succession for Brisbane, who opened the floodgates after halftime to bolt to a 24-8 lead.

The Broncos, who had none of the running in the first half, had managed to head into the main break just two points behind with an 8-6 scoreline despite defending their own tryline for much of it.

Despite that, Cleary said his side looked tired as they struggled to build a lead.

"The first half, I think most teams would have been up more than 8-0, but they just weren't going away. Not just that, but when they got the ball back, they were striking. They seemed to back themselves from all over the field and that took more gas out of our tank than normal. We were more tired than I have seen for ages," Cleary added.

The Panthers' premiership means they become the first team of the NRL era to win three straight premierships.

Despite the incredible scenes and the fact he has "never felt so under the pump", that it wasn't any more special than the other two in their run.

2023 NRL Grand Final - Panthers v Broncos

"They are all as special as each other. It doesn't mean anymore I don't think. It's weird, I don't really reflect that much so forgive me if I can't articulate things very well tonight," Cleary said.

"The way it went though, I've never felt so under the pump in a game for ages as we were in that second half. I thought that the Broncos probably had the better of at least the middle part of the game and probably deserved to be in the lead.

"I suppose though over the course of the last few years that we have won enough games and built enough belief that when we get our momentum going and our game on, good things will happen. I must say though that I was a little worried."