The 610 MW subcritical power plant was originally designed to operate at a constant base load with fixed boiler steam pressure. However, due to grid oversupply conditions, the plant frequently operates at partial loads, resulting in increased inefficiencies caused by throttle losses, particularly during minimum load operations, which significantly reduce high-pressure (HP) turbine efficiency. This study investigates the impact of sliding pressure operation, which involves varying boiler steam pressure with load, on overall plant efficiency compared to constant pressure operation. A virtual plant simulation was employed to model the heat and mass balance of the power plant and simulate operational scenarios under varying steam pressures. The optimal simulation results were validated through direct testing on the plant, followed by performance analysis. The results reveal that sliding pressure operation improves HP turbine efficiency by 5-7%, reduces the net plant heat rate (NPHR) by 57 kcal/kWh, and enhances overall thermal efficiency by 0.35% at 57% load (350 MW).