The quarterback, who played in just two drives in the first quarter, found Victor Cruz for a 57-yard touchdown early in the game.
The 32-year-old told the Giants' official website: "Obviously we got the win, which is nice. [Cruz] had a nice catch and a run for a touchdown. So I think overall, two possessions, two scoring drives, long scoring drives is kind of what you want out of it from the first group. So that was good to see.
"Sometimes that first game you just have to get back to getting used to knowing that the defense can hit you now. You get used to practice and they can't touch you so you're just getting your feet settled and those things and that's what you're looking at.
"Obviously I think I can improve on that. These next weeks should get better and better throughout the preseason. You kind of like to get tackled or hit a few times in pre-season to get used to that for the regular season."
Manning completed two of his five attempts for 73 passing yards during the 18-13 victory.