Madison Keys of the United States stunned Wimbledon champion Marketa Vondrousova to reach the semi-finals of the US Open on Wednesday.

Keys, a US Open finalist in 2017, produced a disciplined performance to clinch a 6-1, 6-4 victory in 1hr 26min on the Arthur Ashe Stadium.

The American 17th seed will play second seed Aryna Sabalenka of Belarus on Thursday for a place in the final.

Czech ninth seed Vondrousova, who made history in July after becoming the first unseeded woman to win Wimbledon, was left ruing an inability to convert any of nine break points against Keys.

Keys by contrast seized every opportunity that came her way, converting all three break points she earned to advance to the last four of a Grand Slam for the sixth time.

Keys said the home support had helped her survive Vondrousova's nine break points.

"I love playing here, in front of a home crowd -- you never feel like you can't get out of any situation," Keys said.

The American said she had decided beforehand to go on the front foot against Vondrousova.

"Just being able to stay aggressive and staying on the front foot the whole time," Keys said, who was beaten by semi-final opponent Sabalenka in straight sets when the two met in the quarter-finals at Wimbledon in July.

"It's going to be a lot of hard-hitting, not a lot of long points," Keys said of Thursday's semi-final. 

"I'm just going to buckle up and get as many balls back as I can."

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