From Longman Dictionary of Contemporary Englishbe a hard act to followbe a hard act to followFOLLOWto be so good or successful at something that it will be difficult for the next person, team etc to be as good We’re looking for a replacement for Sue, but she’s going to be a hard act to follow. → follow
Examples from the Corpus
be a hard act to follow• Clearly Amelia was a hard act to follow.• Judith will be a hard act to follow.• Colm Toibin's piece will be a hard act to follow but I suspect you are up to it.• It was a hard act to follow, but the poor did what they could to provide respectable funerals for their dead. 