The 20-year-old Siniakova suffered an early break but fought back against her American opponent by reeling off four straight games to take control of the opener before she broke twice in the second set on the way to a 78-minute triumph.
"It's been a really great week for me and I'm so glad that I won this time because this match was really tough. I didn't play my best but I'm really happy that I did it," Siniakova said at the presentation.
"It's a great start to the year for me. I hope my performance continues to go up and get better."
The 39th-ranked Riske lost her fourth final, including a third defeat in a title decider in China, as her wait for a first trophy since 2014 continues.
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"She was the better player today and for sure deserved to win the title," Riske said.
"I'm very pleased with my week, even if I did lose today. It's a step in the right direction and I look forward to my next tournament and the rest of the year."
(Reporting by Sudipto Ganguly in Mumbai; Editing by John O'Brien)
