Purpose: To analyze the associations between physiological and biomechanical variables with the FINA (International Swimming Federation) points (ie, swimming performance) obtained in 1500-m front-crawl swimming to determine whether these variables can be used to explain triathletes’ FINA points. Methods: Fourteen world-class, international and national triathletes (10 male: 23.24 [3.70] y and 4 female: 23.36 [3.76] y) performed a 1500-m front-crawl swimming test in a short-course pool. Heart rate (HR), oxygen uptake (${\dot{\mathrm{V}}\mathrm{O}}_2$), and blood lactate concentrations were obtained before and after the test. HR was also measured during the effort. Highest ${\dot{\mathrm{V}}\mathrm{O}}_2$ value (${\dot{\mathrm{V}}\mathrm{O}}_2\text{peak}$) was estimated by extrapolation. Clean swimming speed, turn performance, stroke rate, stroke length, and stroke index (SI) were obtained by video analysis. Results: Average 1500-m performance times were 1088 (45) seconds and 1144 (31) seconds for males and females, respectively. HR after the effort, ${\dot{\mathrm{V}}\mathrm{O}}_2\text{peak}$, aerobic contributions, total energy expenditure, energy cost, and turn performance presented moderate negative associations with swimming performance (r ≈ .5). In contrast, respiratory exchange ratio, anaerobic alactic contribution, clean swimming speed, stroke length, and SI were positively related, with clean swimming speed and SI having a strong large association (r ≈ .7). A multiple stepwise regression model determined that 71% of the variance in FINA points was explained by SI and total energy expenditure, being predictors in 1500-m front-crawl swimming. Conclusions: Swimming performance in triathletes was determined by the athletes’ energy demands and biomechanical variables. Thus, coaches should develop specific technique skills to improve triathletes’ swimming efficiency.