(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 Sjögren'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 didn'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.