Karolina Muchova defeated Romania's Sorana Cirstea in straight sets to reach the semi-finals of the US Open on Tuesday.

Czech 10th seed Muchova advanced to the last four of a Grand Slam tournament for the second time this season with a 6-0, 6-3 victory in 1hr 38min on the Arthur Ashe Stadium court.

Muchova, who reached the final of the French Open in June, will play sixth seed Coco Gauff of the United States in the last four.

The 33-year-old Cirstea had been playing in the quarter-finals of a Grand Slam for only the second time in a professional career that began in 2006.

The Romanian appeared to be caught cold early by Muchova, who punished every mistake ruthlessly to go up a double break for a 3-0 lead in the first set.

Cirstea attempted to rally in the fourth game but despite earning nine break points was unable to convert any of them as Muchova held serve for 4-0.

Cirstea was broken again in the fifth game and Muchova held once more to take the first set.

Cirstea made a better fist of the second set, holding and earning a break to go 2-0 up.

But she was unable to build on that early momentum and was broken in the third game to put the set back on serve.

The decisive break came in the seventh game, when Cirstea found herself 0-40 and then plopped a tame forehand into the net to hand Muchova a 4-3 lead.

Muchova then held before breaking Cirstea in the ninth game, sealing victory with a superb forehand winner.

rcw/mw