Petra Cetkovska has staved off a comeback from Caroline Wozniacki to dump the number four seed out of the US Open in the second round.

Wozniacki started the game strongly as she raced into a 2-0 lead by breaking the Czech in her first service game.

However, Cetkovska levelled the scores with two breaks of her own and then capitalised on further errors from the number four seed to take a 5-4 lead before holding out to win the set.

In the second set, the world number 149 continued to outplay Wozniacki, breaking in the first game and racing into a 3-0 lead as the Dane struggled immensely with unforced errors.

The 25-year-old showed spirit to break back, but Cetkovska hit back immediately to take a 4-1 lead.

However, Wozniacki won the next three games to pull herself back from the brink of defeat and she used her new-found confidence to tie the match by taking the set 7-5.

Both players managed to regain their composure in the third set and held their serve, despite their previous struggles. Wozniacki carved out two match points, but Cetkovska kept the Dane at bay to force a tie-breaker.

The 30-year-old found her best form in the tie-breaker and produced quality groundstrokes to secure her victory with a resounding 7-1 win and with it a place in the third round of the tournament.

Cetkovska will face number 26 seed Flavia Pennetta in the third round of the competition.