NEW YORK, Aug 28 (Reuters) - Ninth seed Daniela Hantuchova became the highest seeded casualty in the women's singles at the U.S. Open on Tuesday when she was upset 6-4 3-6 6-1 by Ukrainian Julia Vakulenko.
The Slovak made 32 unforced errors as she suffered her earliest exit at Flushing Meadows since she lost on her debut in 2001.
"Obviously it was not my best performance today," Hantuchova said.
"I had my opportunities but I think she played very well, especially in the third set. I had my chances and didn't take them."
World number 50 Vakulenko took the first set but the ninth seed looked back on track when she levelled at one set apiece.
However, Vakulenko then broke the Hantuchova serve twice to clinch victory and set up a second-round match with Croat Jelena Kostanic Tosic.
Having ended last year as the world number 18, Hantuchova hit top form in March, winning her second career title at Indian Wells and has reached four semi-finals this year.
However, an illness in Los Angeles earlier this month set her back and she lost her first match in New Haven last week.
"I felt fine here," Hantuchova said. "I felt very good. Today was just one of those things that is hard to understand."
The Slovak said she still harboured hopes of qualifying for the season-ending Sony Ericsson Championships, for the top eight-ranked players of the calendar year.
"It was not a goal at the start of the year but as I started to do better, it (qualifying) became my number one priority," said Hantuchova, who was 10th in the standings going into the U.S. Open.
"It's going to be tough but I still have chances. I may add a couple more tournaments to my schedule if I am doing well."