BEIJING (AP) -- Defending champion Victoria Azarenka double-faulted 15 times Monday in losing 6-4, 2-6, 6-4 to Andrea Petkovic in the first round of the China Open.
''It was an awful match and a very bad performance from me, so there's not much to say about it,'' Azarenka said. ''It happens once, twice a year to every player, and it happened to me today.''
In the men's draw, Lleyton Hewitt knocked out seventh-seeded Tommy Haas 7-6 (6), 6-3 in the first round. Bernard Tomic, Fabio Fognini and Philipp Kohlschreiber also advanced.
In doubles, wild-card entries Serena and Venus Williams lost 6-7 (3), 6-4, 11-9 to Liezel Huber and Chan Hao-ching. Serena Williams double-faulted on match point, then slammed her racket against the court three times before tossing it aside.
Azarenka, ranked No. 2, was broken five times. It was the second straight tournament in which she lost her first match, having been beaten by Venus Williams in Tokyo last week.
Petkovic reached the China Open final in 2011.
''I was happy with my movement and my serve for the most part, and I managed to get a lot of balls back very deep and very strong,'' she said. ''Parts of the match were a really, really good level. Some parts I lost a bit of energy, but overall I'm very happy.''
Eighth-seeded Jelena Jankovic rallied for a 1-6, 6-4, 6-0 win over Anastasia Pavlyuchenkova, who double-faulted nine times. Jankovic had lost three of her four previous matches against Pavlyuchenkova. Jankovic won this title in 2008.
Jankovic's Serbian compatriots Ana Ivanovic and Bojana Jovanovski joined her in the second round. Ivanovic defeated Flavia Pennetta 7-6 (9), 6-1, and Jovanovski downed Sorana Cirstea 6-3, 6-2.