Williams, ranked 14 in the world, is no stranger to being upset by Bondarenko - the 28-year-old Ukrainian having beaten her when the American was third in the world in Toronto in 2009.

Bondarenko - who retired from the circuit at the end of 2012 before returning two years later - looked to be cruising at 6-4, 5-2 before 35-year-old Williams rediscovered her touch and fighting spirit and battled back to even serve for the set. However, Bondarenko -- a highest ranked 29 in 2009 - woke up from her mini slump and won 11 of the last 15 points to take the match.

"I gave my best efforts today," Williams said after the match.

"Your first match is never perfect. She's played matches in the qualication and just never missed today, making great shots all game long.

"I'm really sad. I came here to play and to win but I ran into an opponent that was just too hot today. On a day like today I'm upset - it's normal, it's human. I calm myself down and focus and come back. That moment is that moment. We move on."

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