Novak Djokovic is out of the Australian Open in stunning fashion. The 24-time slam champion medically retired immediately after dropping the first set of his semifinal match against No. 2 Alexander Zverev in a tiebreak 7-6 (5).

America's Tommy Paul faces Germany's Alexander Zverev in the quarterfinals at the Australian Open tonight. Here's how to tune in.

Alexander Zverev has reached the Australian Open semifinals for the third time with a 7-6 (1), 7-6 (0), 2-6, 6-1 win over Tommy Paul

However, even with some shaky serving in his first two games, the second-seeded Zverev survived 12th-seeded American Tommy Paul 7-6 (1), 7-6 (0), 2-6, 6-1 in the quarterfinals in Melbourne on Tuesday.