Having opened the tour with victory over France, the youngsters outscored their hosts five tries to one in George.
While head coach John Fletcher rotated his squad - making 14 changes in all - Will Allman retained his place in the back row, joined in the starting XV by another Saint in scrum-half Alex Mitchell.
Second row Alex Moon was among the replacements for the penultimate game of the tour at Outeniqua Park.
The tour concludes on Saturday afternoon against hosts South Africa in Cape Town.
