Muguruza, Radwanska into quarters

Sydney - Wimbledon champion Garbine Muguruza's decision to accept a wild card at the Sydney International has paid off, so far. 

Muguruza, who retired in the third set from her first match at the Brisbane International last week with leg cramps, beat Kiki Bertens 6-3, 7-6 (6) on Wednesday to advance to the quarterfinals. Agnieszka Radwanksa also advanced with a 7-6 (4), 6-0 win over American qualifier Catherine Bellis. 

Leading 2-1 in the first set, Muguruza left Ken Rosewall Arena for what appeared to be a back injury. But she returned to win six of the next eight games. 

"I struggled a little bit today, with my game, the conditions," Muguruza said. 

She entered the fourth day of the tournament as the only female seeded player remaining following second-seeded Venus Williams' second-round loss on Tuesday. 

Muguruza will play the winner of the all-Australian match between Daria Gavrilova and Samantha Stosur for a spot in the final four. 

Radwanska will play either two-time Wimbledon champion Petra Kvitova or Italian qualifier Camila Giorgi for a place in the semi-finals. 

It's the fourth time the 28-year-old Radwanska has reached the quarter-finals in Sydney. 

"I really like the courts here," Radwanska said. Obviously, conditions are tough, sometimes it's 45 Celsius. Sometimes it's so windy. But I think we're all kind of used to that," she said. "It's something ... in the air that it suits me." 

In men's play, Paolo Lorenzi upset top-seeded Albert Ramos-Vinolas 6-3, 7-5, and Fabio Fognini defeated Alexandr Dolgopolov 3-6, 6-3, 6-4. 

In other second-round results, Daniil Medvedev beat Jared Donaldson 6-3, 4-6, 7-5, Benoit Paire defeated Leonardo Mayer 6-2, 3-6, 6-1 and fifth-seeded Adrian Mannarino beat Ricardas Berankis 6-2, 6-1.

Results from the ATP/WTA Sydney International on Wednesday (x denotes seed):

Men

Second round

Paolo Lorenzi (ITA) bt Albert Ramos-Vinolas (ESP x1) 6-3, 7-5

Adrian Mannarino (FRA x5) bt Ricardas Berankis (LTU) 6-2, 6-1

Benoit Paire (FRA) bt Leonardo Mayer (ARG) 6-2, 3-6, 6-1

Fabio Fognini (ITA x4) bt Alexandr Dolgopolov (UKR) 3-6, 6-3, 6-4

Daniil Medvedev (RUS) bt Jared Donaldson (USA) 6-3, 4-6, 7-5

Alex De Minaur (AUS) bt Damir Dzumhur (BIH) 6-2, 3-0 ret.

Women

Second round

Agnieszka Radwanska (POL) bt Catherine Bellis (USA) 7-6 (7/4), 6-0

Garbine Muguruza (ESP x1) bt Kiki Bertens (NED) 6-3, 7-6 (8/6)

Camila Giorgi (ITA) bt Petra Kvitova (CZE) 7-6 (9/7), 6-2