NEW YORK (AP) — Andrea Petkovic started the day at the U.S. Open Thursday 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…