The purpose of the study was two-fold: (1) to examine the influence athletic performance has on the elements of source credibility, and (2) to investigate its impact on the causal relationships among consumers’ brand attitude, attitude toward the advertisement, and purchase intentions. A between-group experimental design was chosen to assess differences in the source credibility based on an athletic endorser’s on-field performance. Findings identified differences in the elements of source credibility based on an athlete endorser’s on-field performance, while the decomposition of the effects revealed the positive relationship between perceived on-field performance and source credibility. It is necessary to recognize what impact sport celebrity endorsers have in advertising and on endorsed brands based on their current performance, given that the issue of whether or not the sport celebrity’s on-field success affects individual dimensions of source credibility is scarcely addressed in athlete endorsement literature.