This paper tests two hypotheses from the theory of elimination tournaments: (i) that uneven tournaments, where the contestants are ex ante heterogeneous, entail lower effort exertion; this is a prediction from agency theory that has not been tested empirically before; and (ii) whether incentives set through prizes matter for effort exertion; this assumption underlies any agency theory about elimination tournaments, and has been empirically tested in other contexts. The evidence obtained with data from professional tennis tournaments supports both the assumption that incentives matter, as well as the theoretical implications concerning uneven tournaments among heterogeneous contestants.