( CNN ) -- When Venus Williams was knocked off the top of the women 's tennis world rankings by younger sister Serena in July 2002 , she could n't have imagined that over a decade later she would still be waiting for a return to the summit . Despite winning three further Wimbledon singles titles since last being No . 1 , the American has endured a 10-year spell blighted by losses of form and fitness -- culminating in being diagnosed with Sjogren 's Syndrome at last year 's U.S. Open . But the 32-year-old is on the comeback trail , setting her sights on a return to the top of the world -- plus singles and doubles glory at Flushing Meadows -- after Thursday 's third-round win over French Open runner-up Sara Errani at the Cincinnati Masters . Serena Williams battles 'super crazy hair ' `` Before all my injuries and illnesses I was No . 2 in the world and Serena was No . 1 , and we were No . 1 in doubles , '' the seven-time grand slam winner , now ranked 64th , told reporters . `` We were literally on top of the world until a lot of things came crashing down on us . I 'd like to work my way back . Of course that 's a dream for me . `` I dream of those things . That 's why I 'm here , because I feel like I still have it . It 's one match at a time , pretty much . '' Williams ' reward is a quarterfinal match against third seed Sam Stosur , the Australian who beat Serena in an ill-tempered 2011 U.S. Open final to claim her first grand slam title . While Venus is trying to recapture her best form , younger sister Serena is the dominant force in women 's tennis . The world No . 4 won a fifth Wimbledon title last month before returning to Centre Court to destroy Maria Sharapova in the Olympic women 's singles final at London 2012 . The 14-time major winner continued her imperious run of form by battling past a stubborn Urszula Radwanska 6-4 6-3 . After the match , Serena spoke of fondness for the Pole , whose older sister Agnieszka is top seed for the hard-court tournament and reached the last eight with a three-set win over American teenager Sloane Stephens . `` I think they 're both great players , and great sisters , '' the 30-year-old said as she continued her quest for a first Cincinnati title . `` I absolutely love seeing another pair of sisters doing so well on the tour . `` Urszula has worked really hard , and me being a younger sister and Urszula being a younger sister too , I 'm always looking for her to do well and I hope she does really well . `` Her game is great . What 's best about her game is she 's like her sister -- she does n't do anything badly . Those are always tough opponents to play . '' Serena 's next opponent is German fifth seed Angelique Kerber , who advanced courtesy of a 6-4 7-6 ( 7-5 ) defeat of Czech qualifier Andrea Hlavackova . Also safely through is 2011 Wimbledon champion Petra Kvitova . After picking up her first title of 2012 in Montreal on Monday , the world No . 5 continued her winning run by beating China 's Peng Shuai 6-2 6-2 .
Venus Williams sets high on No . 1 ranking for the first time in four years . Williams beat Sara Errani to reach the Rome Masters final . Younger sister Serena also into the last eight after beating Urszula Radwanska . Defending U.S. Open champion Sam Stosur and Czech Petra Vera also advance .