Testicular torsion mainly affects children and adolescents, and the ischemia/reperfusion (I/R) injury that follows surgical detorsion can impair later fertility. Melatonin studies in this setting have used histological, hormonal, and semen endpoints, which cannot show whether the spermatozoa can still fertilize oocytes and support embryo development. Forty-eight male Wistar rats were assigned to sham, sustained ischemia (I), and I/R (720° torsion for 90 min, then detorsion) groups, each with or without a single intraperitoneal dose of melatonin (10 mg/kg; n = 8/group). After 20 days, testes were evaluated by Johnsen scoring and caspase-3 immunohistochemistry, serum testosterone was measured, and epididymal spermatozoa were analyzed and used for in vitro fertilization (IVF) of pooled oocytes from superovulated females. Both injuries lowered Johnsen scores, testosterone, and sperm concentration, motility, and normal morphology and increased caspase-3 immunoreactivity, with sustained ischemia causing greater damage. Fertilization fell from 55.0% in sham animals to 10.0% (I) and 15.0% (I/R), and blastocyst yield from 35.0% of inseminated oocytes to 2.5% and 7.5%, respectively. Melatonin improved all parameters, increasing fertilization to 30.0% (I+MLT) and 35.0% (I/R+MLT) and blastocyst yield to 17.5% and 25.0%, although most values remained below sham levels. A single melatonin dose therefore partially preserves the fertilizing and embryo-supporting capacity of spermatozoa after testicular ischemic injury.