New YORK - World number ones Novak Djokovic and Serena Williams advanced safely to the next round of the US Open on Saturday but the women's draw saw yet another big upset as Wimbledon winner Petra Kvitova was sent packing by a 145th-ranked qualifier.
Third-seed Kvitova fell victim to 21-year-old Serbian Aleksandra Krunic, leaving only three of the top eight women's seeds still in the tournament. Simona Halep (2nd), Agnieszka Radwanska (4th), Angelique Kerber (6th) and Ana Ivanovic (8th) have already been shown the door.
While the women's draw has been ravaged by upsets the top 10 men are still in the hunt, with number three Stan Wawrinka, number five Milos Raonic, eighth seed Andy Murray and number nine Jo-Wilfried Tsonga all moving on.
The shock of the day was delivered by the little-known Krunic, who stung the unsteady Kvitova 6-4 6-4.
The diminutive Serbian, who aims to graduate from university this year with a degree in economics, was a blur as she sprinted and slid into splits while stretching for returns.
"It was an honour for me to be on the same court as Petra, who is a great champion," said Krunic, who will come up against Victoria Azarenka in the next round.
"Of course, I didn't expect to win. Of course, I hoped to. I'm very happy."
Twice Australian Open winner Azarenka secured her spot in the last 16 with a 6-1 6-1 win over Russian Elena Vesnina.
Eugenie Bouchard, a semi-finalist in the previous three slams, including a runner-up finish at Wimbledon, had to fight to keep from joining the list of upsets, the seventh-seeded Canadian holding her nerve to earn a 6-2 7-6(2) 6-4 win over Czech Barbora Zahlavova Strycova.
Williams is the last American standing at the US Open after the remaining home-grown hopefuls said goodbye to Flushing Meadows on Saturday.
A total of 29 Americans (12 men, 17 women) started the year's final grand slam on Monday and by the time the gates to the US National Tennis Centre closed on Saturday only the world number one was still in the hunt for a singles title.
The last two hopes of the men's draw, 13th seed John Isner and Sam Querrey, both bowed out in the third round, while Nicole Gibbs and Varvara Lepchenko also made third-round exits, leaving home fans pinning their hopes on Williams heading into the second week.