A 70-year-old male with anal pain and fever was diagnosed with rectal cancer perforation and abscess in the right gluteus maximus (GM) muscle. He underwent a transverse colon colostomy followed by preoperative capecitabine+oxaliplatin. Some local control was achieved but a residual abscess was observed in the right GM muscle. To secure circumferential resection margin by tumor reduction, he received chemoradiotherapy as total neoadjuvant therapy (TNT) and underwent laparoscopic abdominoperineal resection, D3 lymph node dissection, combined coccyx resection, and partial resection of the right GM muscle. The skin defect and pelvic dead space were filled with a right lateral vastus lateral great muscle flap. Histopathologically, the resected specimen showed no tumor cells in the primary tumor or lymph nodes, indicating a pathological complete response (pCR). This case suggests that TNT might improve the R0 resection and pCR rates and overall survival.