Reigning China Open champion Victoria Azarenka lamented her lack of preparation after crashing out in Beijing at the first stage Monday -- her second early exit from a tournament in a week.
The world number two also blamed her mental fragility for the 6-4, 2-6, 6-4 loss to Andrea Petkovic, a match in which she was often seen cursing to herself as she committed a staggering 15 double faults.
The second seed had earlier in September lost the US Open final to world number one Serena Williams before losing to her sister Venus in the second round of the Pan Pacific Open last week, a match in which she claimed to have felt ill.
The Belarusian said her defeats in Tokyo and Beijing could be attributed to her tough schedule as the season draws to a close.
"I probably should have taken a longer break and just prepare myself," the 24-year-old told reporters after her defeat.
"I don't feel like I was ready to play," she said, adding that "the preparation wasn't there enough, so I cannot deny that.
"It's just my mistakes for not paying much attention after the US Open, how I managed my time and how I managed my health."
Azarenka also said that she felt frustrated in the game against the 2011 finalist, which was held at Beijing's National Tennis Centre.
"In terms of emotions, yeah there was a lot of emotions and frustration that I let myself get into because I wasn't doing the right thing," she said, responding to questions about her talking to herself.
"And with the serve, you know, trying new things, working it during the tournament....it was just off rhythm."
Azarenka rarely showed glimpses of the form which helped her claim the title last year, at times appearing sluggish against the German, who is ranked 43rd in the world.
Petkovic took the first set after breaking serve with the score at 3-3, but Azarenka appeared to be on the ascendency during the second set, taking seven games in a row.
Petkovic needed medical attention after appearing to be dizzy during the second set, but regained her composure in the third set when a double fault from Azarenka left her serving for the match.
China's Zhang Shuai continued her sizzling form, defeating compatriot Peng Shuai 6-3, 6-3 to set up a second-round match against tenth seed Roberta Vinci.
Wildcard Zhang won her first WTA title in Guangzhou earlier this month.
The 24-year-old recruited her own coach in July, following Chinese star Li Na's example in leaving the tightly controlled state sports system, raising hopes that she can emulate the success of the 2011 French Open winner.
It was a successful day for three Serbian players.
Eighth seed Jelana Jankovic needed three sets to overcome Russian Anastasia Pavlyuchenkova 1-6, 6-4, 6-0. Compatriot Ana Ivanovic claimed victory over Italian Flavia Pennetta 7-6 (11/9), 6-1.
Ivanovic had been trailing 5-1 in the first set.
"I really struggled to find my rhythm in the beginning. I felt the ball was flying," she said.
"I didn't really think I could come back in the first set, but I really played well and stepped up when it was very tight, so that gave me confidence."
Bojana Jovanovski rounded off a hat-trick for the Serbians, beating Romanian Sorana Cirstea 6-3, 6-2.
Also in the first round, Canadian Eugenie Bouchard defeated Slovakia's Magdalena Rybarikova 6-4, 6-1 and Russia's Svetlana Kuznetsova swept aside Hsieh Su-Wei of Taiwan 6-1, 6-1.
The men's tournament got under way Monday, but it was heartbreak for the home crowd after China's top-ranked player fell at the first hurdle.
Zhang Ze was knocked out by Australian number one Bernard Tomic 7-6 (7/4), 6-4.
"We were playing juniors matches before and when Tomic was a junior he was sometimes sloppy and he gave many free points," the 23-year-old Zhang said.
"Now he has grown a lot and he is more serious on every single point when he plays."