The assumption that financial incentives are the most powerful lever for driving employee engagement has been increasingly challenged by research grounded in self-determination theory and contemporary organizational psychology. This study examines whether autonomy and purpose—two intrinsic motivational resources—outperform financial incentives in predicting work engagement among knowledge and service workers. A mixed-design study was conducted, combining a cross-sectional survey of 412 employees across five sectors with a randomized vignette experiment (N = 240) that manipulated the motivational framing of a hypothetical role. Engagement was measured using the nine-item Utrecht Work Engagement Scale, while autonomy, purpose, and financial-incentive satisfaction were assessed through validated multi-item instruments. Hierarchical regression revealed that autonomy (β = 0.34, p < .001) and purpose (β = 0.41, p < .001) explained substantially more variance in engagement than financial-incentive satisfaction (β = 0.11, p < .05), with intrinsic predictors accounting for a 22-percentage-point increase in explained variance beyond compensation. The experiment confirmed these findings: participants in the autonomy and purpose conditions reported significantly higher anticipated engagement than those in the financial-incentive condition, with large effect sizes. Results indicate that once employees perceive their pay as fair, additional financial incentives yield diminishing engagement returns, whereas autonomy and purpose continue to generate strong motivational gains. The study contributes empirical support to motivation-crowding perspectives and offers practical guidance for organizations seeking sustainable engagement strategies. Implications for job design, leadership practice, and reward-system architecture are discussed, alongside limitations related to self-report measurement and cross-sectional inference..