World No.1 Simona Halep credits Australian coach Darren Cahill for helping her set up a heavyweight Melbourne semi-final with a straight-sets mauling of Karolina Pliskova.

The Romanian will take on former world No.1 and 2016 champion Angelique Kerber in the final four on Thursday after routing Pliskova 6-3 6-2 in 71 minutes on Wednesday.

Halep had a slow start against the Czech world No.6 and trailed 3-0 before reeling off nine straight games to take command.

Halep said she had to “restart” the match midway through the opening set.

“It wasn’t my best start but I just knew I have to restart actually after three games, to stop missing that much and to move better which I did pretty well in the end,” the 26-year-old said.

“Then I just started to open the court to play my style and I served well today, everything went pretty well for me.

“You (Australians) are very, very relaxed. Darren helps me with that. I am not stressing that much before the matches and trying to start the matches with pleasure and fun and being happy on court.”

Halep, who hadn’t previously progressed beyond the quarter-finals at Melbourne Park, negated Pliskova’s usual booming serve with some superb returns.

The Czech only managed two aces for the match and won just 55 per cent of points on her first serve.

“I am pretty strong on the return, or at least I am practising that,” Halep said.

“It is really good that I can push her back with the return and then I can dominate a little bit more the point.”

Halep has been a semi-finalist at the US Open and Wimbledon and a twice a runner-up at the French Open last year, but a grand slam title has so far eluded her.

"It's really nice to be in the semis… For sure it wasn't my best start, but I knew I had to restart which I did."@Simona_Halep steams ahead to her first #AusOpen semifinal! pic.twitter.com/7gXSSQNdgl

— #AusOpen (@AustralianOpen) January 24, 2018

The in-form Kerber, who crushed Madison Keys 6-1 6-2 in 51 minutes, stands in her way.

“She is moving well and returning the ball good in the court,” Halep said.

“I have to be strong in my legs and be calm and start playing like I did at the end of the match.”

Kerber and Halep have split their previous eight meetings and the German is predicting another long, tight tussle.

“I think it will be a long match with a lot of long rallies,” Kerber said.

“I played against her a lot of times and it was always tough and close.”

The sole grand slam champion remaining in the field, Kerber disarmed the heavy-hitting American with power-punching from the baseline and remarkable consistency.

She made just seven unforced errors for the match.

Kerber felt she was regaining the form that saw her take the 2016 title as well as the US Open crown that year.

“I’m feeling the ball really good and I was enjoying the match,” the 30-year-old said.

“I was going out there and trying to playing my tennis again and it was a good feeling again.”

-AAP