World number one Novak Djokovic had wrist problems again as he lost against Alex de Minaur, a result that helped hosts Australia beat Serbia and reach the semi-finals of the United Cup mixed team event on Wednesday. World number 12 De Minaur beat Djokovic, 6-4, 6-4, in the opening rubber in Perth, and Ajla Tomljanovic then made short work of Natalija Stevanovic, 6-1, 6-1, to clinch matters ahead of the concluding mixed doubles. Like in his previous game against Jiri Lehecka on Tuesday, Djokovic