At that level, it's generally known to be the mental preparation for the given day (along with a bit of luck, as you mentioned).
Indeed, everyone at that level has already been filtered and selected for similar top levels of skill, knowledge, conditioning, equipment, diet, coaches, etc., etc., etc. It comes down to the mental game both internally and between competitors on that particular day.
A classic book to understand some of this is The Inner Game of Tennis by Timothy Gallwey [0]
Source: I formerly competed at international levels for several years in alpine ski racing (mostly DH/Super-G), and studied neuroscience in college as a result of the many fascinating mental phenomena I found in training and competing.
One very interesting fact I came across in neuroscience is that perceptual thresholds for relevant senses, e.g., touch sensitivity for a musician, are about 10X finer than normal people (i.e., they can detect physical differences only 10% the size of that detectable by normal population), and that this is trainable. So yes, this is definitely on the skill/ training side, agreeing with the author.
OTOH, I know some top level musicians who quickly point out that the people with insane levels of desire, motivation, and hard work who will never get to the level to pass a professional audition. But I haven't further data to see what is the issue (does it come to talent, or some genetic shortcoming in their sensory-motor systems, or have they self-sabotaged, or what 20 other factors?)
[0] https://www.amazon.com/Inner-Game-Tennis-Classic-Performance...
The Inner Game of Tennis [0] for folks interested in learning more about this.
[0] https://www.amazon.com/Inner-Game-Tennis-Classic-Performance...
PS Novak's probably more clutch than Rog.
"A guide to a good life" was the first book on stoicism I read, that link was posted before and led me to it, and it really helped me a lot. I would also recommend the "Tao of Seneca" 3 PDFs that Tim Ferriss put together, the audiobooks are great because you can easily listen to a letter a day which helps me to build the habit of following stoicism.
Another book that really helped me was "The Inner Game of Tennis" https://www.amazon.com/Inner-Game-Tennis-Classic-Performance...
The run run run is from an example in the book. I noticed when the Detroit Red Wings were on a losing skid this year players had "skate skate skate" written on the tape of their stick. Also, Roberta Vinci quoted Mindset after taking down Serena Williams at the US Open. And Roger Federer has talked about using a lot of tactics in Mindset.
[1].http://www.amazon.com/Mindset-Mental-Guide-Jackie-Reardon/dp...
[2]http://www.amazon.com/Inner-Game-Tennis-Classic-Performance/...
If you connect with this idea, you may want to check out the book The Inner Game of Tennis: http://www.amazon.com/The-Inner-Game-Tennis-Performance/dp/0...
"Exaggerating Courage" usually works much better than faking it, at least for me, because it's based on a kernel of truth instead of a lie. For example I've never had a tennis lesson but I used to be good at basketball and other sports. So when I'm on the tennis court, even though my technique is poor, I remind myself that I have good hand-eye coordination and agility. So I focus on the fact that "I'm quick!" instead of "My backhand is lame!"
Focus on your strengths, not your perceived weaknesses. Of course when I'm really "in the zone" I'm in a state of Relaxed Confidence where I'm not talking to myself, either positive or negative, and I'm merely reacting to what's required at the moment. It's the ideal mind-body-state to be in when you're trying to return a serve, sink a free throw, hit a fast ball, or in many other non-sports situations. For more on this, check out...
The Inner Game of Tennis: The Classic Guide to the Mental Side of Peak Performance by Timothy Gallwey. http://www.amazon.com/The-Inner-Game-Tennis-Performance/dp/0...
Secondly, your mind is interfering with its own work. Tim Gallwey talks about this in the Inner Game of Tennis (which is not really about tennis! ;). Your critic is not allowing you to "run hot" and put down some words that are less than perfect. It would be helpful to find something to focus your mind on, a simple count, like key strokes or word count. Alternatively, there's the practice of Morning Pages from the Artist's Way. Just let yourself write anything for a while. It's not for publication. You need to open the gates and you can do that by lowering the stakes involved with putting a word on the page.
Inner Game
https://www.amazon.com/Inner-Game-Tennis-Classic-Performance...
Artists Way
https://www.amazon.com/Artists-Way-25th-Anniversary/dp/01431...
I wrote about some other stuff here that helps.
https://vonnik.substack.com/p/a-few-ideas-that-made-my-life-...