The COVID-19 pandemic has moved university teaching and learning activities that conventionally take place in physical classrooms to online platforms. There is an urgent need to investigate university students' experience and perceptions of online learning during the pandemic so as to optimize online learning strategies in tertiary education during and after the pandemic. Based on self-determination theory and the social cognitive perspective, the present study investigated the relationship between perceived relatedness with instructors and classmates, online self-regulated learning (OSRL), perceived learning gains, and satisfaction of 572 Chinese undergraduate students. Through structural equation modeling (SEM) and bootstrapping, we found: (1) relatedness was positively associated with OSRL; (2) relatedness had no direct effect on either perceived learning gains or satisfaction; (3) OSRL has a full mediating effect on the relationship between relatedness and perceived learning gains; (4) there was a serial mediating effect of OSRL and perceived learning gains on the relationship between relatedness and satisfaction; and (5) task strategies and goal setting contributed most to OSRL's mediating effects. Our work provides university instructors, online course designers, and online platform providers with new insights into the importance of supporting undergraduate students' OSRL (particularly task strategies and goal setting) via developing social connections for improving their perceived learning gains and satisfaction in online learning environments.