The Army of South Vietnam (ARVN) did OK in the Battle of An Loc, which was the central battle in the Easter Offensive of 1972, but I don't know if I would say they did "well". The Battle of An Loc was part of the aftermath of the Battle of Loc Ninh, which was a disaster for the ARVN, and truly showed their weaknesses.
At An Loc, Three Vietcong and North Vietnamese Army (NVA) divisions attacked the ARVN 5th Division, which was alone in guarding the main highway to Saigon. By this point in the war, most American ground troops had been withdrawn and operations severely limited. Most of the American power remaining were Air Force bombers and strike fighters, which would prove crucial.
What the ARVN did well was to hold at An Loc and essentially blunt the advance of the NVA until American air power could strike decisively. They also had a great deal of American advisers with them to help direct and coordinate the defense. Knowing they had air supremacy and American help, the ARVN performed more admirably than it would do three years later, in the final offensive that ended the war.
American B-52s were the most effective force during this battle, and the North Vietnamese also learned that any offensive against the South had to have secure logistical support in order to succeed.