But victory was far from straightforward for the former Wimbledon champion.
The 19-year-old Riske had never won a match in a main WTA tour event before this tournament but, after Sharapova threatened a quick victory by taking the first set 6-2, the teenager levelled the match with a 6-4 second set win.
However, she could not maintain that level of play and Sharapova won the deciding set 6-1.
The second seeded Russian will now face top seed Li Na in the final.
However, the Chinese was also taken to three sets in her semi-final before beating France's Aravane Rezai 6-1, 3-6, 6-3.
Sharapova, 23, lost to Li in last year's semi-finals and is looking forward to the chance of revenge.
"It'll be good to play her again," Sharapova told the BBC.
"A year makes a big difference. I certainly don't like losing to the same person twice in a row - I'm a big competitor," Sharapova, also a former US and Australian Open champion, added.
Riske, the world number 185, gave her more celebrated opponent a tough test and an impressed Sharapova said: "I had one sloppy game in the second set and let her back into the match and credit to her she did a great job of executing that set.
"I definitely had to change a few things around in the third set and step it up a bit. I came through in the end and played good tennis.
"My game is trying to attack. If I'm doing it well, I should be winning the majority of my matches and that definitely gives you confidence."