Simulating competition is easy. Simulating the pressure you could feel being center stage at the Big show is harder to do.
Control of the cueball mastery can be easier than Control of the mind.
My personal progress through the development of my pool game started with the physical. My study of the sports with a Willie Mosconi book and included many more, with Billiards As It Should Be Played by Willie Hoppe getting extensive study.
The weakness in my mental game showed when I started playing in the White Spot weekly 9 ball tournament. I recall thinking, "I will be fine as soon as my hands stop shaking." Then the thought hit me with, "they ain't gone stop shaking Until I Make A Ball."

Well learning to shoot with them shaking was my first goal.
The Fight or Flight emotion can generate a focus that the users of cocain find through chemistry.
My personal experience with that emotional distress came when I was first courting the gal that's been my wife ever since. It was at the H bar B Saloon in the cowboy capital of the world. I had long hair and a beard. And was riding a full dresser Harley. We were playing a game of partners 8 ball with the bull dogging Champions. (You know the guys that jump off the back of their running horse to grab the horns and wrestle the steer to the ground). So anyway it was last call on Friday night and I had spent every dollar I had. As I prepared to break she told me, "This is for a 6 pack of Michelobe to go." Well I was young and dumb and preceeded to break the balls without reply. The visions of sugar plums in their heads was in the Christmas song. The visions of blood were in my mind as I broke the rack. The fight or flight emotion was real and I broke and ran the rack. My first win For Money Ever.
Well looks like I am in Novela mode now.

So my training playing the Big Guns in the 9 ball weekly tournament took a while. After a year and a half I won a beer for 7-8.

Eventually I was able to win it. Which led to my personal best performance in the twice a year White Spot Big Show 9 ball event.
I was playing for The Point of the two day event. I went down 6-2 going to 7. I had run to the 7 or 8 multiple times and didn't finish.

So as I was racking for my opponent On the Hill my self to self talk went something like this. " You have handed him game after game. This IS The Big Show and perhaps this guy has never been on this stage before (either). So how about if I just quit handing it to him and make him earn his final game." The chances of me winning 5 before he got 1 more was so slim that I had accepted the loss but just endeavored to go down with Honor. You know that martial arts, "die with honor" attitude that could be oh so powerful. Of course my friends $5 token bet on me at the start of the match had me, uh well not giving up.
Sure enough accepting the inevitable cleared my mind of any negative or nervousness. The next thing I remember is the score was 6-6 and I had a combination on the 9 directly after my last break. My extensive practice of the break shot (the most important shot) paid a dividend. Well there were a few early 9 balls in my comeback but my focus on each task left no brain cells available to remember afterwards anything other than the final shot.
Edited: for clarity.