Caroline Wozniacki of Denmark celebrates after winning match point against Duan Yingying of China at the US Open tennis championships in New York, Aug 27, 2013. [Photo/Agencies]

Former world number one Caroline Wozniacki reeled off five consecutive games to dig herself out of a hole on Tuesday and safely reach the second round of the US Open.

With her boyfriend, Northern Irish golfer Rory McIlroy, watching from the stands at Arthur Ashe Stadium, Wozniacki was forced to work overtime to beat Chinese qualifier Duan Yingying 6-2 7-5.

"It was just difficult because there was a lot of wind out there," said Wozniacki.

"I just kept my focus and kept fighting for every point. She just went for it, hitting everything, and I just had to keep steady and keep running balls down."

Wozniacki seemed to be in cruise control after she raced through the opening set in just 35 minutes but the Danish sixth seed soon found herself in trouble, trailing 5-2 in the second.

But she quickly regained control and won the next five games on the trot to seal victory and avoid a repeat of her first-round exit from Flushing Meadows a year ago.

It was anything but a perfect performance from Wozniacki but she said she was just pleased to advance after her shock early exit 12 months ago.

"I think everyone that you asked today would just say it was a day of survival and a day to get through," she said. "It's not about being pretty. It's about just getting the job done. I did that, so I'm happy about that."

Wozniacki reached the final at Flushing Meadows in 2010 and was a semifinalist each of the next two years but has fallen on lean times since, failing to make it past the fourth round in each of her past six grand slams.

Professional golfer Rory McIlroy of Northern Ireland watches his girlfriend, Caroline Wozniacki of Denmark, as she plays Duan Yingying of China at the US Open tennis championships in New York, Aug 27, 2013. [Photo/Agencies]

The 23-year-old's relationship with McIlroy has been heavily scrutinized but Wozniacki said she remained confident of getting back to her best.

"I always believe in that, so I never lost the belief. There is still so many matches to go, so I just have to go one match at a time like always," she said.

"I think if you ask any athlete, there will always be ups and downs. The downs just make the ups even better. You appreciate it more. You love it.

"I love proving people wrong, and I love what I do. I live the life I have always dreamed of and I have a passion and I have something to wake up for every morning."