Interventions involving exposure to nature can increase self-regulatory resources. However, this improvement has never been examined in mentally fatigued soccer players who have insufficient resources to self-regulate and maintain specific performances. The present study aims to investigate how exposure to nature influences the self-regulation capability of university soccer players who are mentally fatigued. The participants aged 18-24 years (M = 20.73 ± 2.00), with an average training duration of 5.14 ± 1.31 years, were randomly divided into six different groups (three experimental groups and three control groups). Each experimental group was compared with its corresponding control group using three different intervention durations: 4.17 min, 8.33 min, and 12.50 min. A forty-five-minute Stroop task was used to induce mental fatigue, followed by the intervention. The indicators of self-regulation, both physiological (heart rate variability, or HRV) and psychological (competitive state anxiety), were recorded. Experimental Group 3 (12.50 min intervention) only showed significant improvement in HRV (p = 0.008, d = 0.93), competitive state anxiety (cognitive and somatic anxiety p = 0.019, d = 0.86; state confidence p = 0.041, d = 0.797) compared to control group 3. Nature exposure significantly improves self-regulation in mentally fatigued soccer players. Specifically, the 12.50 min intervention showed the greatest improvements in both HRV and competitive state anxiety, suggesting that a longer duration of nature exposure enhances mental restoration more effectively.