The 21-year-old Polish qualifier added to his wins against Philipp Kohlschreiber, Marin Cilic and Andy Murray when Janko Tipsarevic retired during their match on Friday with Janowicz leading 3-6 6-1 4-1.
"This is something magical for me. I don't know what is going on in my heart right now," said the world number 69.
"I feel like I am going to wake up and everything has gone. It is going to take some time to understand what is going on, but I have to focus on my next match."
Janowicz will now meet Frenchman Gilles Simon for a place in Sunday's final.