Caroline Wozniacki has cleared one of the major hurdles in her bid to win the US Open after easing past an error-prone Maria Sharapova, who is still battling to regain her best form after struggling with injuries for the past two seasons.

Sharapova was soundly beaten 6-3 6-4 but contributed to her own downfall with 36 unforced errors and nine double faults, including three in successive points.

A surprise finalist 12 months ago but the top seed this year after the withdrawal of injured world number one Serena Williams, Wozniacki reminded everyone of just how far she has come.

"I definitely think I've improved a lot, not only physically, but also I believe in myself more. I believe I can do it," Wozniacki said.

Wozniacki's next opponent is Dominika Cibulkova, the only unseeded player left in the women's draw.