Self-report correlational data support self-determination theory's (SDT's) postulate that there are three basic psychological needs, for autonomy, competence, and relatedness, which combine additively to predict well-being and thriving. However, experimental research in the SDT tradition has focused only on autonomy support, not relatedness and competence support. To fill this gap, we employed a 2 x 2 x 2 factorial design within a game-learning experience to predict rated need satisfaction, mood, and motivation, and also objective game performance. Manipulated competence and relatedness support had main effects on most outcomes. Rated competence, relatedness, and autonomy need satisfaction also predicted the outcomes, and the significant experimental main effects were all mediated by the corresponding rated variables. Neutral control group data showed that thwarting participants' needs is more impactful than enhancing them. These findings offer new support for key postulates of SDT, while integrating the correlational and experimental traditions in this area.