The fundamental goal of education is to teach students to become self-regulated learners who actively and efficiently manage their learning processes by deploying self-regulated learning strategies. Based on this stance, the present study investigated whether these strategies predicted the writing performance of English major students. Eleven students enrolled in the Advanced Writing Skills I course at Bahir Dar University in the 2024/2025 academic year participated in this study. An interrupted time-series within-group design, by which a single group is measured multiple times both before and after the intervention, was employed. Repeated measures of ANOVA, narration, and textual analysis were used to analyze the data obtained from argumentative writing tests, diary entries, and essay excerpts, respectively. A univariate ANOVA results (F(2.295, 50) = 73.657, p < 0.05, [partial eta-squared] = 0.880) revealed a significant effect of self-regulated learning strategies on writing performance. Moreover, diary entries indicated that the implementation of these strategies in EFL writing was effective in enhancing students' writing skills. These included organization (introduction, body, conclusion, formulation of thesis sentence), mechanics, grammar, and cohesion. Regarding their progress across time, significant improvements in writing skills were observed in the first diary compared to the baseline data. Significant progress was also reported in the second diary, surpassing previous records. Additionally, textual analysis of the essays supported the finding that students made significant progress in their writing performance after the intervention. The students indeed believed that the instruction on self-regulated learning strategies was motivating, encouraging, commendable, and loving. Thus, the instructional process needs to incorporate these strategies along with the micro-analytic protocols.