You do realize he's hitting the majority of the notes just fine, right? He goes softer or more piano on a few, which is just being a good musician and creating sound dynamics, not lowering his pitch. He's even recovering that ghostly, serene falsetto he used to have, as clearly evidenced by the opening seconds of his performance. As for being "drowned out by the drunks in the audience", the camera being used to record it all isn't of the greatest quality, and the guy drowning him out is right next to the camera and screaming his lungs out, so unless Don is supposed to be Graham Bonnet, no shit he's getting drowned out. Don is all the way up on stage, this guy is a good few rows back, and much closer to the camera's already low quality mic than Don.
