MELBOURNE: Defending champion Novak Djokovic showed yet more mental and physical resilience to beat German sixth seed Alexander Zverev and reach the Australian Open semifinals on Tuesday. The top seed fought back to win 6-7 (6-8) 6-2 6-4 7-6 (8-6) in Melbourne. The Serb will face Russian qualifier Aslan Karatsev, who beat an injured Grigor Dimitrov, on Thursday. Karatsev, ranked 114th in the world, is the first man in the Open era to reach the last four on his Grand Slam debut. Few will fancy Karatsev ––- who largely plies his trade on the second-tier ATP Challenger Tour ––- to continue his dream run by beating eight-time champion Djokovic. The 33-year-old world number one looked far from comfortable against Zverev, largely down to the German’s big serving and probing groundstrokes, rather than the abdominal injury which has bothered him throughout the tournament.