Andrea Petkovic started the day at the U.S. Open with an upset, beating No. 6 seed Petra Kvitova 6-4, 6-4.
Kvitova, a two-time Wimbledon champion, could never get into a rhythm from the baseline or the net and piled up 32 unforced errors. The last came on match point, when Kvitova shanked an overhead off her racket frame wide.
For Petkovic, a German ranked No. 88, it was only the second time she has scored back-to-back main draw victories this year.
Next up for Petkovic is either No. 25 Elise Mertens or Kristyna Pliskova.
In other early results, 15th-seeded David Goffin beat Gregoire Barrere 6-2, 6-2, 6-2 in less than an hour and a half, and No. 20 Sofia Kenin downed Laura Siegemund 7-6 (4), 6-0.
