In Oncology, chemoresistance is often responsible for therapeutic failure. In this work where we used human cancer models, we investigated whether precise metabolic changes could account for chemoresistance. Not only in cisplatin-resistant ovarian cancer but also in temozolomide-resistant glioblastoma, we evidenced highly oxidative chemoresistant phenotypes depending on mitophagy. Consequently, inhibiting either mitophagy by more largely blocking autophagy or cell respiration by targeting Complex I in the electron transport chain with olaparib allowed to resensitize cancer cells to cisplatin and/or to temozolomide. We propose that these two approaches used in combination therapies with selected forms of chemotherapy would be attractive for countering cancer chemoresistance.