NEW YORK (Reuters) - Greek Maria Sakkari broke down twice Grand Slam champion Petra Kvitova's defences 6-4 6-3 to reach the fourth round of the U.S. Open on Saturday.

The 17th seed relied on her powerful serve once again, winning all but one of her first-serve points in the first set and firing off nine aces in the match as she never conceded a break on Arthur Ashe Stadium.