The increasing use of self-paced computer and web-based platforms for e-learning and work has led to renewed interest in promoting intrinsic motivation. A classic finding in motivation literature is the undermining effect: Task interest is reduced when previously presented monetary rewards are eliminated. Efforts to prevent undermining effects on web-based tasks have focused on adding game-like features, such as points or leaderboards (i.e., “gamification”), to maintain task interest. On the other hand, some have raised the concern that these game elements could be a reward that undermines intrinsic motivation, such that task engagement is reduced when these game features are eliminated. We, therefore, conducted two preregistered studies of the undermining effects of pay and gamification in a web-based memory task. Results revealed a small undermining effect for task engagement and performance when previously presented incentives were removed from the task. Exploratory analyses suggested slightly different mechanisms behind each type of undermining effect. Finally, we observed large benefits for engagement and performance of performance-based monetary rewards, relative to adding game elements alone. Implications for explanations of the undermining effect and application to online work and learning contexts are discussed.