"My first ever league game, I loved it. There's more similarities than I thought to the NFL. In terms of style of play, the making of the frontline of players, field position and things like that.
"It took me a while. I was thinking 'now why are they getting the ball back again'.
Mangini, who most recently was defensive coordinator at Jarryd Hayne's San Francisco 49ers, said there was a few things the NFL could learn from the NRL.
"I thought it [the club] was well run especially around the areas of player performance, with the GP tracking. That's just starting to come into American sports. I thought that aspect of it was much more advanced here and much more interactive than anything I've experienced in the States.
"Just trying to get a feeling for the players and I was really really impressed with the toughness of the game, the toughness of the players. the incredible durability of the players... 30 games in the season? That's crazy."
Another aspect of league that Mangini was impressed by was the curtain-raisers.
"It's interesting that they have the two games prior to the main game. That's a full day of football. You can get your money worth."
Mangini said his sons even followed Sunday's game online and the Warriors may have some new fans.