"He took his opportunities. He deserved his big win today," Djokovic said. "It was a tough battle mentally, physically, emotionally obviously. This is what happens when you play a top player on this stage, when you go the distance in the fifth.
"He showed his mental strength and he deserved to win — the only thing I can say is congratulations."
Djokovic hadn't lost at Melbourne Park since 2010, when he went down to Jo-Wilfried Tsonga in the quarterfinals, and has been unquestionably the best player on Rod Laver Arena since 2011.
With his winning streak and his new coach, Boris Becker, he was installed as the tournament favorite immediately after the draw, when he landed on the opposite side to top-ranked Nadal, Wimbledon champion Andy Murray and 17-time major winner Roger Federer. Nadal plays 22-year-old Bulgarian Grigor Dimitrov in the quarterfinals on Wednesday, when Murray and Federer go head-to-head. That leaves all the major winners on one side of the draw.
Berdych, the 2010 Wimbledon finalist, reached his first Australian Open semifinal — completing a full set at that level in the majors — when he beat David Ferrer 6-1, 6-4, 2-6, 6-4. No. 3-seeded Ferrer was clearly frustrated at times, yelling at himself after points and bumping into a line judge after breaking Berdych in the sixth game of the third set.
The 31-year-old Spaniard said it was an accident in a "nervous moment," as he went for his towel, saying "It was nothing ... I say to him excuse me after that."
He could face a sanction for coming into contact with a match official.
On the women's side, 19-year-old Canadian Eugenie Bouchard reached the semifinals in her first trip to the Australian Open, beating Ana Ivanovic 7-5, 5-7, 6-2 to set up a showdown with two-time finalist Li Na.