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Barty took an easy 6-3 victory in the first set over her 14th-seeded American opponent.
In the second set, Keys put up a little more resistance and Barty was only able to break in the seventh game.
That left her needing just two more games to progress to the semi-finals, but Keys broke her opponent for the first time in the match to level at 5-5.
Barty was in just her second Grand slam quarter-final, which may have explained her struggle to close out the match.
However, the eighth seed broke back to establish a 6-5 lead, and she regained her composure to hold her serve and claim victory.