MELBOURNE — It was difficult to tell who was more pleased with reaching the Australian Open semifinals: No. 1-ranked Novak Djokovic, advancing to his 25th at a Grand Slam tournament, or 19-year-old Madison Keys, who beat Venus Williams to get into her first. Djokovic was simply overpowering as he beat Canadian Milos Raonic 7-6 (5), 6-4, 6-2 in exactly two hours at Rod Laver Arena in a night match on Wednesday, never facing a break point.