India, Jan. 29 -- Novak Djokovic was the first to admit he's lucky to be back in the Australian Open semifinals instead of Lorenzo Musetti. Despite being two sets down, slowed by a serious blister on his foot and already thinking about his flight home, the 24-time major winner won Wednesday's quarterfinal when fifth-seeded Musetti retired with an injury.

Musetti took the first two sets 6-4, 6-3 but needed a medical timeout for treatment on his upper right leg after being broken in the third game of the third. The 23-year-old Italian played on for almost two games but couldn't continue.

After serving a double-fault in the fifth game to give Djokovic another breakpoint chance, Musetti wiped a hand across his face, walked toward the net an...