Jenrry Mejia might have finally rediscovered a lost friend. The Mets right-hander was a late arrival to camp this year and has been limited to two Grapefruit League appearances, but the recent reemergence of his signature pitch, the cutter, is making it a successful spring training for him. “I think we actually fixed what we needed to fix,” pitching coach Dan Warthen said yesterday. Mejia, who is battling tendinitis, said he doesn’t know when his next appearance will come, but saw enough Monday when he pitched a scoreless inning against the Tigers to believe the cutter has returned. It’s a pitch that was compared by scouts to Mariano Rivera’s cutter when Mejia first arrived on the major league scene three years ago. “In 2010 I had a real good cutter,” Mejia said. “But then I couldn’t find that. I feel better now.” The rediscovery likely won’t be enough to land him on the Opening Day roster, even if Johan Santana isn’t ready because Jeremy Hefner appears to have dibs on that rotation spot. But at least it gives the Mets hope the 23-year-old Mejia’s best days are ahead of him.