Digital game-based vocabulary learning (DGBVL) integrates key game elements such as Challenges, Rewards, Human-Computer Interactions (HCI), Multimedia, and Fantasy. Although the overall effectiveness of digital games in enhancing English-as-a-foreign-language (EFL) vocabulary knowledge development is well-established, the specific roles of individual game elements remain underexplored. To fill the gap, we developed a DGBVL program incorporating the five elements to examine their impact on learner engagement and vocabulary acquisition among 50 Chinese university students. Data collection methods included an eye-tracker, pre-post-delayed tests, and semi-structured interviews. The results indicated that Challenges significantly engaged learners, while deep engagement in HCI and limited engagement in Fantasy positively influenced vocabulary knowledge development. Our findings refine existing theories on DGBVL by elucidating how game elements individually and collaboratively facilitate learner engagement and vocabulary knowledge development across the phases of Preactional/Forethought, Actional/Performance, and Post-actional/Self-reflection learning.