The 17-year-old Riedewald equalised for Ajax with two minutes left and then scored a stoppage time winner.
Coach Frank de Boer called it a "fairytale" and said he had anguished over selecting the youth team midfielder out of position at left back for his first league match.
"It was Jairo's task to push forward but that he would pop up in the penalty box we certainly did not expect," he told FOX Sports.
Ajax took over at the top from Vitesse Arnhem, who drew with Heracles Almelo on Saturday, on goal difference as the league takes a four-week mid-season break.
Both clubs are on 37 points.