The former Feyenoord striker capitalised on some poor defending find the target five minutes from time and secure all three points to spare goalkeeper Leonard Nienhuis' blushes.
Bob Schepers put Cambuur on course for victory when his left-foot strike from outside the penalty area found the back of the net 17 minutes in, but four minutes later Nienhuis inexplicably dithered with the ball at his feet and Damiano Schet robbed him before sliding the ball into the empty net.
Nienhuis redeemed himself by palming a Sander Duits free-kick against the post, then Martijn Barto restored RKC's lead with a scrappy strike two minutes before the break to take his tally to four goals in his last five games.
The visitors were not finished, though, as French striker Jean-David Beauguel levelled with a neat right-foot finish after 66 minutes.
But Dwight Lodeweges' side were not to be denied and Manu sealed all three points after some dreadful defending from the visitors, who have now lost four of their last five matches and remain third-bottom of the table.
Victory for Cambuur stretched their unbeaten run to six games and they are now up to ninth in the table.
