Swiss 17-time Grand Slam champion Roger Federer advanced to the quarter-finals of the Australian Open with a gruelling five-set victory over Japan's Kei Nishikori on Sunday. Federer will now play Andy Murray's conqueror Mischa Zverev after winning 6-7 (4/7), 6-4, 6-1, 4-6, 6-3 in three hours...