Bhima's weapon is the gada, the mace, and the epic is careful to say that he and Duryodhana learned it from the same teacher, Balarama, who rated Duryodhana the more finished technician. That detail sets up the ending: the two best mace fighters of the age are on opposite sides, and the better stylist is the one who loses.
In the dice hall Bhima swears two oaths. He will tear open the chest of Duhshasana, who dragged Draupadi by the hair, and he will break the thigh of Duryodhana, who bared it and struck it as an invitation to her. Both are fulfilled, and both are ugly. The second is more than ugly, it is against the rules: a mace duel forbids a blow below the waist, and Bhima strikes only after Krishna signals by slapping his own thigh.
The epic does not let this pass. Balarama, who taught them both, is present, rises in fury and has to be restrained from killing Bhima on the spot, and leaves. The victory is won by a foul, prompted by an incarnate god, in front of the teacher of both fighters, and the narrative preserves every part of that rather than smoothing it. Bhima is usually read as the simple one of the five brothers, all appetite and force beside Yudhishthira's scruples, but the moments the epic gives him are precisely the ones where force is made to do what righteousness could not.