Grace along with South Carolinian Ben Powell both claim to have shot a mounted man from his horse. There was indeed another officer who was mounted and shot at about the same spot, but it wasn't Sedgwick. Sedgwick was on foot when he was hit. We really don't know who shot Sedgwick.
What is important that there was a change in command as folks were pushed up the ladder as a result of Sedgwick's death. Two days later Col. Emory Upton attacked a weak point in the Mule Shoe and captured it. However, his attack was unsupported (by Gershom Mott) and it failed. Two days later a larger corps scale assault was tried by Hancock's II Corps. That was a very bloody battle. Some Union soldiers believed that had Papa Sedgwick been around to coordinate either assault, it would have succeeded (Credit goes to Gordon Rhea as the first modern Civil War historian to point this out).
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!