Cincinnati, Ohio  - Kim Clijsters proved her comeback to tennis is serious as the former number-one defeated longtime rival Patty Schnyder 6-2, 7-5 Wednesday to reach the third round of the Cincinnati Open.

The 26-year-old, back on court two years after retiring to marry and have a child, will next face her toughest test so far when she plays Russian eighth seed Svetlana Kuznetsova.

Clijsters showed the spark which took her to the US Open title four years ago in the 70-minute victory, with her second win after re-starting her career this week to determine the state of her form 18 months after giving birth to daughter Jade.

Clijsters managed four aces and never faced a break point, breaking Schnyder three times to improve a career record to six wins and two defeats against the Swiss veteran.

The winner began her return this week with a win against 2007 Wimbledon finalist Marion Bartoli.

Clijsters acted upon her desire to get back into the sport after resuming training for an exhibition series she played last May to mark the debut of the new Wimbledon centre court roof.

The Belgian, winner of 45 singles titles retired in May, 2007 and announced her comeback effort five months ago. (dpa)