Tennis - Sabalenka
Aryna Sabalenka swatted aside Czech Karolina Pliskova to reach her second straight US Open semi-final. Image Credit: Supplied photo

New York: In-form Aryna Sabalenka swatted aside Czech Karolina Pliskova 6-1 7-6(4) to reach her second straight U.S. Open semi-final on Wednesday.

The Belarusian underestimated her opponent in their two meetings last year, when Pliskova defeated her in the Wimbledon and Montreal semi-finals, but she was in dominant form in New York as she fired down seven aces and never dropped serve.

"Always tough matches against Karolina," said Sabalenka. "The first set was really high level for me and (I) put a lot of pressure on her." Nothing went right for 2016 finalist Pliskova during the first set as she racked up 15 unforced errors and five double faults in 28 minutes.

But the Czech's form improved considerably in the second set as she fended off the only break point she faced in the eighth game.

Sabalenka kept her cool in the tiebreak and raised her arms in triumph after sealing victory with a forehand winner on her second match point.

"In the second set, I knew she will kind of trying to come back and she will do better. I just tried to hold my serve and try to put her under pressure on her serve," she told reporters.

Sabalenka said she completely remodelled her serve before arriving in New York, adding another member to her coaching staff in order to change "biomechanic stuff".

"Right now I'm not going for aces I'm just trying to put my serve on the big targets," she said.

"I'm ready for another fight and I think I just have to stay focused on myself." Pliskova had appeared to be in good form after taking down twice Grand Slam winner Victoria Azarenka in the fourth round in New York, and told reporters she had little explanation for her struggles in the first set.

"I was not playing at all the way I was playing the last couple of matches, especially the last one with Azarenka," she said.

"She was playing super-aggressive, serving amazing today. I think I never play her in this kind of shape." Sabalenka will play world number one Iga Swiatek for a place in Saturday's final.