The talented Czech recorded a 6-3 6-4 victory over Riske in the decider in China on Saturday.
In her third final, it marked a first title for 20-year-old Siniakova, while it made it back-to-back defeats for Riske in Shenzhen deciders.
Riske has also lost four consecutive finals as her wait for a second title – and first since 2014 – continues.
"It was a really great week for me and I'm so glad I won this time because this match was really tough for me," Siniakova said.
"I think I didn't play my best but I'm so happy that I did it."
Siniakova had won the only previous meeting between the pair, but she fell behind to an early break.
However, from 2-1 down, Siniakova reeled off four straight games before serving out the set.
She eased into a 4-1 lead in the second set before Riske fought back, but Siniakova closed out her victory.