Caroline Wozniacki upset by Petra Cetkovska at U.S. Open

Caroline Wozniacki was upset by Petra Cetkovska in the second round of the U.S. Open on Thursday.

Caroline Wozniacki was upset by Petra Cetkovska in the second round of the 2015 U.S. Open on Thursday night at Arthur Ashe Stadium.

Cetkovska earned a 6-4, 5-7, 7-6(1) over Wozniacki, who was the runner-up at last year's Open. 

Wozniacki, the tournament's No. 4 seed, got off to a slow start, losing the first set and dropping the first three games of the second. But Wozniacki rallied to force a third set and appeared to have Cetkovska on the ropes. 

Down 6-5 and serving, Cetkovska saved four match points to force a tiebreaker, which the Czech Republic native won 7-1. 

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Cetkovska was also responsible for Wozniacki's second-round exit at Wimbledon in 2013. 

Cetkovska will play No. 26 Flavia Pennetta in the third round. 

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