Novak Djokovic suffered his earliest grand slam exit in 20 years in New York on Sunday and said he doesn’t know the solution to the physical problems he’s battled in “pretty much every match” this year.Argentine Mariano Navone’s 7-6, 5-7, 4-6, 6-2, 6-1 victory in the first round of the US Open ended Djokovic’s latest bid for a record 25th grand slam title.It also ended his run of 78 first-round victories in major tournaments, a streak stretching all the way back to a 2006 loss to Paul Goldstein at the Australian Open.Djokovic vomited on court and struggled with late-match cramps and back pain – an “awful feeling” that he’s becoming used to.“It’s something that I’ve been carrying, unfortunately, pretty much every match this year. Vomiting, throwing up … Then my whole body starts to collapse, basically cramping and pain.”Mariano Navone celebrates after beating Novak Djokovic. Photo: APAlthough he reached the final of the Australian Open this year and the semi-finals at Wimbledon, Djokovic said he’s not equipped right now to go deep in tournaments – and he’s not sure what the fix is.