Marathas were not winning from the beginning, from the very start, Gardi's got too close to right flank of Afghans and made the mockery of himself when his shots were flying above the head of Rohillas for an hour. When he attempted to fight the Rohillas in direct combat, his six battalions got wiped out in the very first phase of battle and he himself got wounded. The Maratha officers like Vithal Shivedv and other officers of their left wing, outflanked gardi and tried to take on Rohilla infantry but were beaten back with heavy losses. I dont need to tell the other details, the point is Marathas started taking heavy losses in the battle from very early on, not due to destiny but due to relatively weak war skills of their commanders and Ahmad Shah Abdali was too good general for them.