Wimbledon champion Petra Kvitova was stunned in the third round of the US Open by a scrambling, moon-balling qualifier ranked No 145.
Aleksandra Krunic, a 21-year-old Serb who until this week had not taken even a set from a player in the top 30, crumpled to the court in celebration and shock on Saturday (local time) when she pulled off the 6-4 6-4 upset of the third-seeded Czech.
"Of course, I didn't expect to win," said Krunic, the second qualifier to pull off such a shocker after 121st-ranked Mirjana Lucic-Baroni beat No 2-seeded Simona Halep on Friday.
After a week of upsets on the women's side, only three of the top eight seeds remain, No 1 Serena Williams, No. 5 Maria Sharapova and No 7 Eugenie Bouchard.
Kvitova, who would have ascended to the No 1 ranking if she won the US Open and Williams had lost before the quarterfinal, committed 34 unforced errors against the fast-moving Krunic, who slid and sometimes went into a gymnastics split to chase down every ball and make her opponent hit one more shot.
Kvitova too often failed to do so, including what should have been an easy putaway of a drop shot. But that went in the net and gave Krunic a point to win the first set. Kvitova sprayed a backhand long on the next point to lose it.
Those problems continued in the second set, when Kvitova bashed a backhand long to give Krunic the break to go up 3-2. Kvitova then sailed a lob long to go down 4-2.
In an epic 27-stroke rally on match point, Krunic looped several towering shots before Kvitova sailed yet another forehand out to end it. Krunic faces the winner of the match between 16th-seeded Victoria Azarenka and Elena Vesnina.
There was no upset for 11th-seeded Flavia Pennetta, who downed American wild-card Nicole Gibbs, 6-4 6-0.
The men's side, meanwhile, remained largely true to form. None of the top 10 and only two of the top 20 seeded men had lost entering Saturday. Tenth-seeded Kei Nishikori continued that trend, advancing in straight sets against No. 23 Leonardo Mayer.
In other key matches Saturday, top-seeded Novak Djokovic faced American Sam Querrey, and fellow American John Isner, seeded 13th, sought to defeat No 22 Philipp Kohlschreiber, the man who has beaten him in the third round the last two years.
For the third time in three matches at this year's US Open, Williams faced an American, this time 52nd-ranked Varvara Lepchenko.
Williams has won 16 matches in a row at Flushing Meadows; she could become the first woman with three straight titles at the tournament since Chris Evert took four in a row from 1975-78.