While the effectiveness of machine translators (MT) has been overtly focused on in L2 writing, scant attention has been paid to students’ actual use of MT in situated educational contexts. To fill this gap, the present study explored how two Korean college students with different levels of English proficiency utilized MT for composing an English text. Students were asked to participate in a series of writing sessions, where they wrote English texts with the help of MT at their discretion. A variety of data were collected for qualitative analysis, including questionnaires, student texts, reflection journals, and interviews. It was found that students exhibited divergent strategies to take advantage of technological affordances. The main purpose of MT use by the more proficient student was to construct cohesion and coherence in writing and search for sophisticated vocabulary, whereas the other student used MT mainly for identifying and addressing her difficulties in terms of grammar and vocabulary. Despite their different purposes of MT use, both students took MT as a self-directed learning tool. These findings shed light on the educational potential of MT, which could be implemented in a writing classroom to assist not only English learners, but also instructors.