Maria Sharapova forced to dig deep by Riske in Shenzhen Open

The five-times grand slam champion fired 34 winners and saved seven out of 10 break points to get past her spirited opponent and set up a quarter-final clash with Kazakhstan's Zarina Diyas who beat local hope Zhang Shuai 6-3 6-7(5) 6-4.

Twice a finalist at Shenzhen, Riske used power and precision to breeze through the first set and went up 2-1 in the second to leave Sharapova in trouble. The Russian then reeled off five of the next six games to level the contest at one set apiece.

Sharapova did not let the momentum slip in the deciding set, winning the final four games of the match to prevail in two hours and 22 minutes.

"I'm glad I got this kind of match," Sharapova said. "These are the kind of matches you need, especially with such a short preparation going into the Australian Open in terms of match play.

Earlier, Kristyna Pliskova, the twin of former world number one Karolina Pliskova, stunned French Open champion Jelena Ostapenko 6-1 6-4 and stormed into the second round.

World number seven Ostapenko, who beat returning multiple major champion Serena Williams in an exhibition match in Abu Dhabi over the weekend, was undone by Pliskova's powerful serves.

"My serve was great today, especially in the first set," the world number 61 said after her second career win over a top 10 opponent. "I feel like it's fast here, so that can be tricky for both of us, and the first of us playing fast won the point."

Pliskova next takes on Romania's Ana Bogdan, who comfortably defeated Italy's Camila Giorgi 6-4 6-2.