This study quantifies the concept of momentum in sports, inspired by Novak Djokovic's unexpected loss in 2023, and evaluates its impact on game outcomes. Utilizing a structured multi-index approach, we categorized performance into fourteen primary and three secondary indexes. The TOPSIS model enhanced by entropy weighting, along with the Delphi model, was applied for weight assessments of these indexes. Our analysis, incorporating the Mann-Kendall trend test and Spearman correlation coefficient, revealed a significant correlation of 0.51 between momentum and match results, underscoring its pivotal role. The results contribute to a deeper understanding of momentum, enabling coaches to refine strategies and optimize performance based on dynamic changes in momentum. This study provides a comprehensive framework for quantifying momentum, with potential applications extending beyond tennis to other sports where strategic momentum management could influence outcomes.