Nole completed Nole-Slam when he won 2016 RG. That kind of four in a row GS trophies was neither achieved by Fed nor by Ralph. Surely, that would have been pressure filled situation as well. But, he managed to do it. So, I don't really buy that he will buckle under pressure.
I am not claiming that Novak will actually complete the CYGS. But, I am of the opinion that if he does not, it will be because his tennis was not good enough and he was outplayed as opposed to he buckling under pressure. Come on, Serena lost to a doubles player Roberta Vincy who was unknown even in doubles. The comparable thing is something like Novak losing to Rajiv Ram in Singles - that ain't going to happen.
Yes, he completed the Nole Slam, in 2016, when Fedal were not much there to block him. But he DID buckle rather immediately afterwards. After two very strong rounds at Wimbledon that year, he fell to Querrey, and it has to be said it was clear that a lot of that was mental, on his part. I'm just saying, he's susceptible to the pressure.
As to Vinci, you are wrong about her. First of all, she was in the SFs. And she was a very good doubles player. She won 5 GS doubles, so just because YOU don't know her as a doubles player apparently means nothing. While none of us thought that Serena would lose to her, pre-match, here is why I think Vinci was the perfect person to take her down in that match, which is related to why I think Querrey was the perfect person to take out Novak at Wimbledon in 2016. If you watched the Williams v Vinci SF, Serena started nervous, with heavy legs. Vinci, a veteran, and a great doubles player, was not over-awed by either Serena, or the moment. She saw that she was nervous, and kept her moving those heavy legs. She won that match on experience, and guile and by moving Serena front to back, not just giving into side to side.
Sam Querrey, likewise, I think was perfectly placed to take out Novak in W. 2016. He's experienced, he was having some great serving, and he was chill enough to wait for the opportunities. No one saw that coming, and it did remain the upset of the year on the ATP side. Was it all Querrey? No.
So you insist that Novak will only lose at the USO if his tennis is not good enough. I'm saying that the pressure is going to be a thing, and the right player at the right moment can catch him up. His tennis is spectacular, no doubt. And if he withstands the pressure, the physical and emotional fatigue, and all comers, including Nadal, who will be fresher, well, good on him. But there are a lot of minefields, (mind fields?) to get there, as Serena can tell you.