Well, I think you did more than the right thing. I have never discussed a game with my opponent before it actually happens...but you did, and you gave him a heads up that you were going to fight it till the end. So your friend was warned to bring his best game. What was his reaction after you beat him? Are you still friends ;)

 He was very upset before the game and more upset after the game. Then he became more friendly after a month and we played a match which I won. Then a little later he said he was in trouble and wanted me to loan him some money. I stupidly did loan him money and after that he stopped playing in tournaments and I never saw him again. I did notice [later] he made USCF master. :)