The Frenchman -- who is aiming to be the first player from his country to win the tournament since Jo-Wilfried Tsonga in 2009 -- came back from a set down to triumph over top seed Cilic 6-7 (5), 6-4, 6-0.
Victory over the Croatian brings Mannarino his first ever win over a member of the world's Top 5 and he will face an equally tough test in the final where he will meet World No. 11 David Goffin.
The fourth seed moved another step closer to booking his place at the ATP World Tour finals next month as he reached his second final in as many weeks after seeing off Argentinian Diego Schwartzman.
Despite winning the encounter in straight sets, the Belgian did not have it all his own way with the World No. 29 taking him to two tie breaks in his 7-6 (3), 7-6 (6) win.
Goffin -- who was runner up at last year's tournament -- is looking for his second successive win on Asian soil after claiming his first title in three years at the Shenzhen Open last weekend.
If Mannarino can claim another surprise win in Sunday's final, it would not only be the 29-year-old's first win over the Belgian, but it would also see him earn his first ATP Tour title.