One of the most sensitive changes faced by universities due to the COVID-19 crisis was the remote assessment of student learning. This research analysed the case of a massive distance learning university that rapidly changed the final assessment (N=126,653 undergraduate students in 2020) from face-to-face exams to entirely online exams. The research focused on the influence of online assessment on academic performance and students' perception of the new method. Two data sources were used: the contrast of academic performance indicators (assessment, success and achievement rates, and average marks obtained) between the online examination call and the previous ones with face-to-face examinations; and a questionnaire to a sample of students (n=714) on their perception of the online assessment experience. The results show that all the academic performance indicators in the 28 Bachelor Degrees offered at the university increased when the final assessment method turned to online due to the pandemic crisis; and that a majority of students are more favourable to online assessment methods. The discussion places these findings in a context of rapid change, and concludes by identifying the possible implications of online assessment for student retention, organisational challenges, as well as possible further studies.