Nothing to forget when it's only in your mind, and South Vietnam was always losing (ridicalous battles of even the "elite" forces like the VN Rangers with American air support being massacred in their hundreds by the outnumbered and of course outgunned VC). It's pretty hard to find an early battle that wasn't a VC victory. There was never any period during 1961-65 (the "pre-Marines" American involvement) when Saigon was winning, reversing the ever increasing communist gains. "Even" the Strategic Hamlet Program was hugely counterproductive, and so was the 1963 coup.

South Vietnamese started getting their shit together only later, with one of their greatest moments ironically during the final collapse (and while left all alone):

The last major battle of the Vietnam War was fought at Xuan Loc, only 37 miles east by northeast of Saigon. In April 1975 the town was the eastern anchor of South Vietnam’s final line of defense against the North Vietnamese rush to the capital. That line ran west through Bien Hoa, just north of Saigon, to Tay Ninh, near the Cambodian border. Once it broke, Saigon was doomed—and with it the Republic of Vietnam itself. When the North Vietnamese Army attacked Xuan Loc (pronounced Swan Lock) on April 9, the communists and almost everyone else expected the Army of the Republic of Vietnam’s 18th Division to collapse like a house of cards, as had so many other ARVN units during the NVA’s massive Spring Offensive of 1975. But ARVN forces under Brig. Gen. Le Minh Dao fought fiercely in a last-ditch effort to save their country. By the time Xuan Loc did fall 12 days later, most of the world was amazed at how well the ARVN had fought, and the NVA had paid a far steeper price than it expected. Indeed, the valiant stand at Xuan Loc by heavily outnumbered ARVN soldiers echoes the famed sacrifice of King Leonidas’ 300 Spartans facing Xerxes’ Persian masses at the Battle of Thermopylae in 480 B.C. Greece. The Persians then marched south and captured Athens.