New York: World number one Caroline Wozniacki came back from a set and 4-1 down to defeat Svetlana Kuznetsova and reach the US Open last eight on Monday just as her lofty status again looked too heavy a burden to bear.

The Dane, who is still searching for an elusive Grand Slam title to support her top ranking, saw off the tiring 2004 champion Kuznetsova 6-7 (6/8), 7-5, 6-1 and will now tackle Germany's Andrea Petkovic for a place in the semifinals.

It was a huge struggle for the 21-year-old Wozniacki on a night of fluctuating fortunes on Arthur Ashe Stadium in a gruelling 3hr 2min encounter which finished 2330 local time (0330GMT).

She surrendered a 5/2 lead in the first set tiebreak and then slipped 1-4 down in the second set before 15th-seeded Kuznetsova's game fell to pieces.

Wozniacki evened the contest on a third set point in the second set and then clinched breaks in the first and fifth games of the decider.

Kuznetsova, who was undone by 78 unforced errors, saved four match points in the seventh game but Wozniacki took victory with a smart backhand volley.

"I thought about the match we played against each other here in 2009. I was a set and down in the second in that one and still won," said Wozniacki.

"I knew I could come back so I just stepped into the lines and went for my shots, tried to make fewer errors. I am in good shape. I can play for five hours if I have to. I just wanted to keep the rallies going."