The Serbian was pushed all the way to five sets in Melbourne before eventually winning 12-10 in the fifth.
Djokovic believes that the 28-year-old Swiss is now producing his best tennis on a more consistent basis.
"It's definitely one of the most exciting matches I have played in my life on this surface, that was played on a very, very high level," Reuters quotes the 26-year-old as saying.
"In the past we all knew that he has the quality to play that well, but not in a consistent basis.
"He's a very complete player. He can play equally well on any surface. He had one of the best seasons in his life."
A place in the final awaits the winner of Saturday's match.