Tsitsipas – ranked seventh in the world – beat his German opponent 7-6 (8-6) 6-4 in one hour 51 minutes.
The Greek booked his place in the final on his sixth match point to defeat the world number six in Beijing.
He will face Austrian top seed dominic thiem, who beat Karen Khachanov, in Sunday’s decider.
Thiem battled back from a set down to beat the Russian 3-6 6-1 6-1 earlier on Saturday.
Meanwhile, Britain’s Jamie Murray and partner Neal Skupski missed out on a place in the men’s doubles final, losing 6-4 6-4 in 76 minutes to Croatia’s ivan dodig and Filip Polasek of Slovakia.