Resumo. ABSTRACT This study compared the frequency, number of goals and attack efficiency in temporal numerical superiority among winning and losing teams and among balanced and unbalanced matches in a junior men’s water polo competition. Another analysed relationship was that between a balanced or unbalanced final score and the efficiency at scoring goals in numerical superiority in the winning teams’ games. A total of 56 matches from the Pan-American Junior Men’s Water Polo championship was analysed. The teams were categorised as losers or winners and the match results were classified as balanced or unbalanced. The chi-squared and Mann-Whitney tests were used for statistical treatment. There is no significant difference in the occurrence of numerical superiority between winners and losers (p = 0.25) despite the winners scoring more goals (p = 0.002) and being more efficient (p < 0.001). There is no significant difference in the occurrence of numerical superiority (p = 0.81) and goals (p = 0.03) in balanced and unbalanced matches. However, there tends to be a higher shot efficiency (p = 0.01) in unbalanced matches. A significant relationship exists (p = 0.04) between the winning teams’ efficiency at scoring goals in a situation of numerical superiority and an unbalanced score.