Background <p>Mental preparation is a fundamental aspect of athletic performance. We present here an experiment aimed at evaluating the effectiveness of a blended intervention to promote mindfulness and self-confidence and a reduction of anxiety among professional athletes.</p> Methods <p>The intervention, delivered through an application for smartphones, included eight weekly modules with variable and progressive training and relaxation exercises. Meetings with the athletes took place every 2 weeks. The study involved 41 tennis players who were randomly assigned to either the intervention or the control group. Data were analyzed via repeated measures ANOVA.</p> Results <p>The results showed a significant change in self-confidence, arousal control, anxiety, awareness and refocusing in the experimental group and no significant change in the control group.</p> Conclusion <p>The blended intervention showed good results in only 8 weeks, thus again emphasizing the effectiveness of breathing and relaxation techniques opening the door for future studies and interventions that can use new technologies to promote athletes’ well-being and performance.</p> Trial registration <p>Current Controlled Trials NCT06212986, 01/18/2024 - Retrospectively registered.</p>