Defending champion Novak Djokovic overcame a brief blip to book his place in the semi-finals of the Australian Open with a four-set victory over Tomas Berdych on Tuesday. The world No. 1, drawn against the world No. 6 for the right to face David Ferrer (who had earlier defeated Nicolas Almagro) for a berth in the Melbourne final, paid the price for some woeful serving in the second set - but roared back into the ascendancy after ironing out whatever issue was afflicting him to secure an eventual 6-1 4-6 6-1 6-4 win.