SHANGHAI :Fourth seed Novak Djokovic battled past a spirited Zizou Bergs 6-3 7-5 on Thursday to reach the Shanghai Masters semi-finals for a 10th time, setting up a clash with surprise package and world number 204 Valentin Vacherot. In challenging conditions, Djokovic was made to work harder than the scoreline suggests by his Belgian opponent, who actually registered more winners than the four-times champion but was undone by unforced errors. "First encounter with Bergs, a great guy. Obviously