As long you play the best tennis you're capable of, you can hold your head high.
hold (one's) head (up) high
To feel and show pride in oneself, especially in times of difficulty, failure, or embarrassment. I know you're unhappy that you lost, but you should hold your head high and be proud of all you accomplished this season.No matter the outcome, they can hold their heads up high that they did a good job on this.