Tennis-Ivanovic ousted in U.S. Open first-round upset

* Ivanovic had left foot taped midway through the final set * Cibulkova to play qualifier Jessica Pegula in second round (Adds quotes) By Larry Fine NEW YORK, Aug 31 (Reuters) - Former world number one Ana Ivanovic was the first major casualty of the U.S. Open as the Serbian seventh seed lost 6-3 3-6 6-3 to Dominika Cibulkova in the opening match at Arthur Ashe Stadium on Monday. Ivanovic, the 2008 French Open champion and a semi-finalist at Roland Garros this year, fell victim to an unlucky draw as the 50th-ranked Cibulkova of Slovakia was ranked in the top 10 last year before slipping after an Achilles-related surgery. "It was a very tough matchup, I thought, especially for the first round," said the 27-year-old Serb. "It's definitely very disappointing, because I felt like I did a lot of hard work over last few months. Over the last week, I had great preparation, lots of good training and everything." Cibulkova seized the advantage with a service break in the fourth game of the third set for a 3-1 lead and consolidated it with a backhand drop shot to make it 4-1. A backhand long from Ivanovic, who had her blistered left foot taped midway through the final set, ended the nearly two-hour contest. "Today I know that my game was there on the court," said 26-year-old Cibulkova, who was coming off a quarter-finals berth last week in New Haven. "I just had to stay tough and know I had to do it, she doesn't give away shots." Cibulkova, a 2014 Australian Open finalist, will next face American qualifier Jessica Pegula, a 7-5 6-3 winner over Belgian Alison Van Uytvanck. For Ivanovic, the result continued an up-and-down season. She reached the semi-finals at Roland Garros this year and was coming off back-to-back quarter-finals at U.S. Open tune-up events in Toronto and Cincinnati. She also has lost three times to players outside the top-100 this year, including twice at grand slams. "I really felt like I had been improving. Last week I saw a huge improvement in my game overall. My serve was really good today," said Ivanovic. "It was very tough first match I think for both of us. First match of the tournament, as well." (Editing by Frank Pingue)