NEW YORK (AFP) - Novak Djokovic makes his case to be ranked atop the greatest champions in tennis history at this year's US Open, where he seeks an unprecedented 21st men's Grand Slam singles crown.

The 34-year-old Serbian, who began playing tennis at age four after swinging a mini-racquet as a toddler, will also try and complete the first men's singles calendar-year Grand Slam since Australian Rod Laver in 1969.