Gamified online quizzes have gained popularity for their potential in enhancing student learning motivations, creating engaging lessons, and improving learning outcomes. Yet, its application and effectiveness in support of student vocabulary learning have only been explored in synchronous learning setting. This study, hence, extended the exploration by examining the implementation of gamified vocabulary learning in an asynchronous mode and analyzing the impacts on students' learning outcomes in class. The study was carried out for 10 weeks, involving 300 2nd year students at a Thai university. The instrument and measure comprised 500 English academic words made into 10 vocabulary sets on "Quizizz.com," and 10 in-class vocabulary tests. The findings of the study revealed that students' vocabulary learning practice in asynchronous mode had positive correlations with and could significantly predict their in-class vocabulary results. Female students outperformed male students; nonetheless, there was no significant difference across academic majors.