Scotland's Peter Nicol, who beat the seventh seed, Chris Walker of England, believes he is the man to upset the Pakistani, who is chasing his eighth Hong Kong title.
Cairns, ranked 12th, could not live with the controlled, error-free play of the world No 1 and said afterwards that squash needed someone to put the frighteners on him.
"He is always odds-on favourite to win events and that is not good for the sport," Cairns said. "We need somebody to really push him. At the moment he does not think he can be beaten. The sport needs a player to get a win over him to put that bit of doubt in his mind."
Nicol, the fourth-seeded Scotsman, beat Walker 15-8, 15-13, 13-15, 15- 9 to set up a semi-final with the world No 2, Rodney Eyles of Australia.
Nicol, one of the elite few who has beaten Jansher in a major tournament, said: "I am fully fit for the first time in more than a year.''