Shenzen, Auckland: Maria Sharapova was made to work hard for a victory at the Shenzhen Open, rallying from a set behind to beat unseeded American Alison Riske 4-6, 6-3, 6-2 in the second round on Tuesday.

The five-time 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 No. 1 Karolina Pliskova, stunned French Open champion Jelena Ostapenko 6-1, 6-4 and stormed into the second round.

World No. 7 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 No. 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.

Biggest win

Caroline Wozniacki capped 2017 with the biggest win of her career when she claimed a maiden WTA Finals triumph in October and the Dane has carried that momentum into the new season with a ruthless display to kick off her Auckland Classic campaign.

The top seed has a chance to usurp world No. 1 Simona Halep with a victory in New Zealand and the 27-year-old needed just 58 minutes to race past American Madison Brengle with a 6-3, 6-0 triumph in their first round encounter on Tuesday.

The world No. 3 is still searching for her first grand slam triumph but after emerging victorious in the elite eight-woman event in Singapore, her raised levels of play could see her make that breakthrough in Melbourne later this month.

Wozniacki is also searching for a first triumph in Auckland after reaching the final in 2015 and despite being tested by Brengle early the contest, the Dane pulled away once she found her rhythm and claimed the last seven games to seal victory.

“I thought I played pretty well, especially considering it’s the first match back of the year,” Wozniacki told reporters. “It took me a couple of games to kind of just get the rhythm and then I started playing better and better.

“I’m just trying to get my legs moving, trying to make the right decisions, wait for the right shots to play aggressive and go for it, and find the right balance of offence and defence.”

The win set up a second round encounter against Croatia’s Petra Martic, who overcame Czech player Marketa Vondrousova 7-6(2), 6-3 in their first round tie to advance.

Elsewhere, former world No. 2 and 2013 Auckland champion Agnieszka Radwanska was forced to dig deep to remain on a semi-final collision course with Wozniacki when the Pole eked out a 6-2, 4-6, 6-2 victory over Brazil’s Beatriz Haddad Maia.

“I’m just very happy to win my first match of 2018, and I think it was good timing to come back and do it here in Auckland after five years,” Radwanska, who has seen her ranking drop to 28th after a poor 2017, said in her on-court interview.