Purpose: To assess efficacy, safety, and tolerability of the preservative-free (PF) fixed-dose combination (FC) of tafluprost 0.0015%/timolol 0.5% (PF tafluprost/timolol FC) in treatments-naive patients with primary open-angle glaucoma (POAG). Methods: This was a retrospective, real-world clinical practice setting study that included 107 eyes of 107 subjects with POAG who had never been treated for glaucoma. All subjects were received PF tafluprost/timolol FC once daily. Intraocular pressure (IOP) levels were documented for each eye at the untreated baseline and up to 6 months after the initiation of medical treatment. All adverse events, including ocular and systemic adverse reactions, were recorded. Additionally, the reasons for medication discontinuations were thoroughly documented. Results: A total of 32 POAG patients with high-baseline IOP (>21 mmHg) and 75 with normal-baseline IOP were included in the study. The subjects’ baseline mean age was 62.4 ± 8.7 years (range, 26.0–85.0 years); among them, 42 were female (39.3%). Mean IOP at baseline for all patients was 18.6 ± 4.3 mmHg. The mean IOP at 6 months was 12.6 ± 4.7 mmHg, representing a significant decrease compared to the baseline (–32%, p < 0.001). In POAG patients with high-baseline IOP, mean IOP was significantly lowered from 28.0 ± 5.7 mmHg at baseline to 18.0 ± 5.5 mmHg (–35%, p < 0.001); in patients with normal-baseline IOP, from 14.6 ± 3.4 mmHg at baseline to 10.3 ± 4.1 mmHg (–29%, p < 0.001). PF tafluprost/timolol FC was well-tolerated and safe. After 6 months, 97.2% of all patients remained on therapy. Conclusions In this real-world observational study, once-daily treatment with PF tafluprost/timolol FC demonstrated clinically relevant and statistically significant efficacy, as well as safety and good tolerability, in treatment-naive patients diagnosed with POAG.