SYDNEY - Romania's Simona Halep fought off big-serving Czech Karolina Pliskova to reach the semi-finals of the Sydney International on Wednesday.

The world number two had been tested in two tight previous matches, and Pliskova again made things difficult for Halep. Halep had early breaks in both sets only to be pulled back, before the tournament top seed closed out for a 6-4, 7-5 win over the Czech fifth seed in one hour and 38 minutes in blistering heat.

"It was tough today. Was very close. She's playing well, and she's strong with the serve," Halep said. "I expected that she's going to hit all the balls, so she did. Against her you don't have rhythm too much, so that's why it's tough to play."

Halep finished with slightly more winners than Pliskova, 22 to 21, but far fewer errors, 33 to 43. The Romanian is battling an Achilles injury and admitted to feeling pain during her opening victory over Frenchwoman Caroline Garcia late Tuesday. It followed her late withdrawal from the Brisbane International last week. Halep will face former world number two Svetlana Kuznetsova in the last four after the Russian fought back from 1-5 down in the opening set to knock out Italian Sara Errani 7-6 (7/1), 6-0. Halep leads Kuznetsova 3-2 in their previous meetings.

"I know that she's playing a lot of topspin, so it's a different player tomorrow, different style," Halep said of facing Kuznetsova. "I expected a tough one. Of course every match at this level is very tough, but I believe I have my chance."

Elsewhere Puerto Rican qualifier Monica Puig ended Australia's Samantha Stosur's run, 6-4, 6-4 and will face eighth seed Belinda Bencic in the semis after the Swiss beat Russian Ekaterina Makarova 6-0, 2-6, 6-4 in an evening match. "It's a very important win for me coming through three rounds of quallies and obviously coming through in the main," Puig said. "I've lost to her twice before, so it was a pretty big win for me today considering the amount of times I played her."

Dimitrov to face Dolgopolov in quarters:Grigor Dimitrov reached his second consecutive quarter-final of the new season with a straight-sets win over Uruguayan Pablo Cuevas at the Sydney International on Wednesday.

The Bulgarian world number 28, looking for more matches under new coach Franco Davin, ousted Cuevas 7-6 (7/2), 6-4 and will next play Ukraine's Aleksandr Dolgopolov in the quarters.

Dimitrov, who reached a career-high ranking of eight in 2014, lost in three sets to Roger Federer in the quarters of last week's Brisbane International. "I think right now I need to play more matches, as many matches as I can get early on in the year," Dimitrov said.

"It's going to help me with my ranking, but also with the level that I'm trying to achieve. I've worked a lot on a lot of things this off-season, so I just want to make sure I put them into play and just make them as a habit. That's the thing that is very important to me."

Dimitrov took the opening set in 51 minutes after a one-sided tie-break, and then opened the second set with his only break of the match. That was all he needed as he worked his way to victory in one hour 37 minutes. The Bulgarian will face Dolgopolov in the quarters after the Ukrainian knocked out American qualifier Alexander Sarkissian 7-6 (8/6), 6-2. "Dangerous player. Never know what to expect. Especially here. The conditions are pretty suitable for him," Dimitrov said of Dolgopolov. "It's a faster court and a little bit windy. So it's going to be definitely a tricky match for me."

Australia's top seed Bernard Tomic claimed a quarter-final spot in the tournament for a fourth straight year with a 6-2 6-2 romp over compatriot Jordan Thompson in just 48 minutes in the evening match. "I think always looking back it was my first title here, so the memory is always there. With the memories comes the confidence," Tomic said. "I feel so good playing on that court. Every time I step on that court I know this is where it all started for me." The 2013 champion will face Russian Teymuraz Gabashvili in the quarters. In other matches Wednesday, Luxembourg's Gilles Muller was leading second seed Dominic Thiem 7-6 (7/2), 2-2 when the young Austrian retired with blisters on his right foot.

Thiem was coming off a semi-final loss to Federer in Brisbane. Muller, a Sydney semi-finalist last year, has now dropped just seven points on his first serve over two matches, in defeating young guns Thiem and Croatia's Borna Coric.

Muller, who also reached the fourth round of the Australian Open last year, will face Frenchman Jeremy Chardy in the quarters. Sixth seed Chardy ousted Australian James Duckworth 7-6 (7/5), 6-4, while French qualifier Nicolas Mahut downed fifth-seeded Italian Andreas Seppi 6-3, 1-6, 6-3.

Other Wednesday winners were Gabashvili, 6-3, 6-3 over Argentina's Federico Delbonis, and Serbian third seed Viktor Troicki, 6-1, 6-4 over Spaniard Tommy Robredo.