Although competition is regarded as a powerful motivator in game-based learning, it might have a negative influence, such as damage to confidence, on students who lose the competition. In this paper, we propose an indirect approach, substitutive competition, to alleviate such negative influences. The approach is used to develop a My-Pet v3 system, in which pupils master subject materials to make their pets stronger, and compete against each other. Specifically, pupils learn Chinese idioms in a pet-training game scenario, and their mastery of the material is related to the pets' strength to win the competition. The result of the competition is influenced by whether pupils spend enough effort on the learning tasks. This intention is expected to alleviate the negative influence that results from direct competition. A within-subject experiment was conducted to examine the influence of substitutive competition. The results indicated that substitutive competition seems a promising scheme to maximise the power of competition. However, there were no apparent evidences in this study to demonstrate its effect to alleviate pupils' sense of failure, as compared with other two direct competition conditions.