Raghu triumphed because he found the other players in the game.
It was clear that Raghu was able to discover the players who were hiding. Desai writes, "Raghu had found all the others long ago." His physical strength helped him. His long "footballer" legs enabled him to outrun the other players who sought to find the "den," or the safe place. His height enabled him to see where the other kids were hiding. He was skilled at finding players, like Manu, with relative ease.
Raghu's sense of strength and skill marginalizes Ravi, his brother. The tiny boy knows that he will never be able to compete with the likes of his brother. Physically, he is not as mature yet. At the end of the story, tiny Ravi is not able to mount a credible defense so that he might win the game. Everyone accepts that Raghu has won. Even the maternal Mina rejects Ravi's claims to victory. The kids have understood that Raghu triumphed, and they proceeded to play "another and another."
Desai constructs Raghu's victory as inevitable. Ravi is not going to taste the vindication of a victory of his own. The facts that no one takes him seriously and that everyone accepts Raghu as the inevitable victor hurt Ravi even more than his loss. It is Raghu's strength and ability to silence dissent that make his triumph over all other players a foregone conclusion.