WARSAW, May 3 (Xinhua) -- Defending champion Kim Clijsters slumped to a 7-6 (3), 6-3 defeat against Ukraine's Julia Vakulenko in the second round of the Warsaw Cup WTA tennis tournament on Thursday.

Clijsters, second seed of the tournament, was never able to get the upper hand against an enterprising opponent that she beat easily at the same stage a year ago.

It was the last match Clijsters will play in Warsaw and one of her last ever. The Belgian confirmed her decision to retire from the tour at the end of this year.

"It seemed to me like I did not play any worse than I did last year at this time, just as the clay court season was beginning," Clijsters told reporters after the match.

"The only difference was Julia's serve, she served extremely well and played an over all good match. She hit really hard, close to the lines and did not make many mistakes. I was always on the back foot, always defending and unable to attack," she added.

"I still have not decided what I will do in the future. I am now going back home to my fiance and my dogs," Clijsters said.