Juan Martin del Potro believes Novak Djokovic can end his career as the most successful Grand Slam title winner, surpassing Roger Federer-s current mark of 20. Djokovic clinched his third US Open title on Sunday with a 6-3, 7-6 7/4, 6-3 triumph over del Potro, taking him level with Pete Sampras-s mark of 14 Grand Slams.

The 31-year-old Serb is now just three behind Rafael Nadal and six back from Federer. "Of course he can," said Del Potro when asked if Djokovic can claim the record over Federer who is six years his senior.