The cortisol (C) and testosterone (T) responses to experimental stress have been linked to sport and health outcomes several days to years later. Here we examined the utility of these biomarkers, taken across a simulated Olympic weightlifting (OWL) competition, as predictors of future competitive performance in young athletes. Seventy junior athletes (46 males, 24 females) participated in a talent identification and development programme that replicated an OWL competition. Performance was indexed by the total load lifted, relative to body mass, with serum changes in C (∆C) and (∆T) concentrations profiled. We identified each athlete’s best performance in real competitions over two subsequent years via online resources. Hierarchical regression was used to predict changes in competitive performance at <12 (∆Total12) and 12-24 months (∆Total24). The simulated OWL event promoted a small positive ∆C (effect size [ES]=0.3) and ∆T (ES=0.5), but with large variation in ∆C (-58% to 200%) and ∆T (-21% to 71%). Performance improved after 12 (ES=1.5) and 24 months (ES=0.9). The ∆C was negatively related to the ∆Total12 and ∆Total24 when controlling for competitions entered (R2=13-24%). Sensitivity analyses confirmed the ∆C link to both outcomes (R2=9%). The serum C and T responses to a simulated OWL competition varied considerably between participants. Their competitive performance improved over the next two years and individual performance trajectories were related to the ∆C. Therefore, individual variation in the C responses to a competitive stressor may help forecast the training and/or competitive gain process in young developing athletes.