From my observation, there are two types of athletes: "Trainers" and "Performers." Performers are the ones who are born with a natural talent for handling pressure. They are the ones who play better in the match than during training and who hit aces and winners during important points.
For example, Carlos Alcaraz is a prime example of a Performer. I was so impressed with how he handled himself during the US Open at such a young age. He won the US Open because he played the critical points better than his opponents, which is what it comes down to. The mindset is what separates the best from the great. When competing at such a high level, everyone knows how to move and hit the ball well. Everyone has put an incredible amount of blood, sweat, and tears into the sport and made many sacrifices. The key difference is how one handles the nerves and game during the most critical points - game points, breakpoints, and matchpoints.
Being a natural performer like Carlos is rare. Most people are not born with this talent, but it doesn't mean you cannot be one of them. Becoming a Performer is a skill that one can learn. It needs a lot of discipline, persistence, and consistency in practicing the mindset, but with time and hard work, you will be able to re-wire your thoughts and how your brain looks at critical situations. Here are some tips:
1. Being nervous is a good thing. One of the most important things is to realize that if you are nervous, it means you care. And if you care about what you do, you want it to turn out well. You want to win - whatever winning means for you and your specific situation. It means that what you do is where your passion is. It is something you highly care about and want to be good at it. Good job for finding something you are passionate about and which inspires you to be better!
2. Nervousness and excitement live very close to each other. You can find a substantial amount of literature that argues the close connection between feeling anxious and excited. From my perspective, it is almost as simple as the label you choose to put on the feeling. The power is in framing the situation and recognizing it for what it is: "What an amazing opportunity to practice my skills. This is why I have been working so hard. Now go out there, and put your whole heart and soul into it. Stay present, get focused, be active." These are some of the words that help me. I encourage you to create your own. Experiment with this and see what works for you. The most important thing is to focus on the opportunity and the positive. Direct your sentence towards the process - not the outcome you want or don't want to achieve, as that can trigger more tightness and nervousness. For example, I strongly recommend avoiding things like: "I want to win this point. Just don't double-fault. One more point, and I will win the match!" These sentences are not productive as they tend to get you away from the present moment. If you get a thought like this, try clearing your mind as quickly as possible - you must act as if the thought never existed!
3. Get grounded, stay relaxed, be present! Here is where you have to know what you already know. You put a lot of work and effort into something; you must believe you are great at what you do; get out of your own way and let the body do its own thing - perform! Keep things simple - don't overthink. Stay in the moment, and clear your head of unproductive thoughts. And by unproductive, I would argue that most thoughts in these critical moments will be unproductive - try to think about nothing at all - empty space! Here is where I found that my meditation practice has helped me. Meditation helps you practice how to clear your mind and get rid of thoughts that don't serve you. Getting into a space of emptiness and pure focus is where you want to be. Trust your body; trust your instincts. Let the body and muscle memory do the work they have been trained to do. If tension comes, one thing that has always helped me is to narrow down my focus on what I can control. If the opponent hits a fantastic shot, that is outside of what I can control. The only thing I can control is how I move and the shot I hit. If I focus on staying loose and focused, it will come naturally.
Lastly, I find that learning how to think and control your mind is way more difficult than training your muscles and body to create specific muscle memory. It requires serious consistency, perseverance, and continuous practice. There will be setbacks, but there will be progress. Stay with it; as you practice, it will become easier and more natural. Trust the process. While this article is written from a tennis player's perspective, you can adapt these steps to any other sport or performance. I find the same process can be helpful for anything from sports to important business meetings, to interviews or public speaking performances.
Here are some resources with more information on this topic (forward to minute 45).