( CNN ) -- Venus Williams claimed her first singles title in more than two years with a straight sets victory over Monica Niculescu of Romania Sunday to win the Luxembourg Open . The 32-year-old American has slipped down the rankings after battling SjÃ¶gren 's syndrome , an auto-immune disorder that causes fatigue and joint pain . But the seven-time Grand Slam champion put that behind her with a 6-2 6-3 scoreline in the final for her 44th career singles crown on the WTA Tour . Younger sister Serena tweeted : My eyes are watering up because I am so proud of my sister @ Venuseswilliams so proud of you sis congrats on your tournament win ! I . The pair had combined together in the London Olympics to win the women 's doubles gold for the third straight Games , with Venus showing signs she was returning to her best . A semifinal victory over rising young German player Andrea Petkovic confirmed her form and fitness in a two-hour 38 minutes battle Saturday and Niculescu proved an easier victim in the title match . She made a string of errors to lose in the Luxembourg final for the second straight year . Serena Williams is in the field for the WTA Championships in Istanbul next week , her first tournament since winning the U.S. Open title last month . Venus will go ahead to prepare for the 2013 season and the opening Grand Slam of the season in Australia . `` Coming to the tournament this week I was just trying to play well . I did n't know if I could win this event , so to stand here as the winner is a wonderful way for me to end the year , `` she told the official WTA website . `` It really makes me look forward to next year as well . '' Meanwhile , in the final of the Kremlin Cup in Moscow , former World No.1 Caroline Wozniacki beat top seed Samantha Stosur of Australia 6-3 4-6 7-5 in a grueling final . Dane Wozniacki was claiming her 20th career title but her first Premier Level event in 14 months which have seen her slip down the rankings . In the ATP event in Moscow , second seed Andreas Seppi of Italy came from a set down to beat fourth-ranked Thomaz Bellucci of Brazil to win the title . The 28-year-old Seppi prevailed 3-6 7-6 6-3 for his third career title and second of the year . Argentina 's Juan Martin del Potro secured the Austrian Open title and kept up his bid to make the ATP Tour Finals with a 7-5 6-3 defeat of qualifier Grega Zemlja in the final . Del Potro has been out for a month with a wrist injury but the victory left him seventh in the points race with the top eight qualifying for London next month . Tomas Berdych of the Czech Republic also looks set for the end of season finale after beating top seed Jo-Wilfried Tsonga of France 4-6 6-4 6-4 in the final of the Stockholm Open . Berdych holds sixth place in the standings with Tsonga in the eighth and final spot .
Venus Williams wins Luxembourg Open title . First singles title for 2010 Austrian since 2010 . She has battled a disorder which affects the auto-immune system . Kremlin Cup takes Caroline Wozniacki in London .