[Valin]

Actually I think day 1 was the decisive day. When Ewell didn't take Cemetery Hill.

[MikefromOhio]

No that was a critical day, and certainly Buford's action in front of Heth saved the day, and in the end the battle, as the battle lines were drawn from where Buford was holding when Reynolds came up, not to mention Ewell's failure, but the CSA could have still won the battle had they not charged directly up Little Round Top. They could have easily swung around to the right and taken the entire Union Army from the rear.

[Redleg Duke]

Gettysburg is an interesting battle in that there were a series of "key points" where it could have gone one way to the other. It was probably the first battle where the Union got it mostly right. Holding the high ground on Day 1, Little Round Top and the Center on Day 2 set up a situation where Lee lost it on Day 3 and ordered Pickett's Charge.

The South suffered from "Victory Disease" and the Union commanders managed to identify and accomplish their individual missions in such a sequence the they kept missing blowing it!