ISTANBUL - Even though she won four big titles during the year, Serena Williams will still end 2012 ranked number three behind Victoria Azarenka and Maria Sharapova.

Serena Williams of the US celebrates with the trophy after her victory against Russia's Maria Sharapova after their final WTA tennis championships match in Istanbul, Oct 28, 2012. [Photo/Agencies]

After backing up her victories at Wimbledon, the Olympics and the US Open with the WTA Championships title on Sunday, Williams concurred with Sharapova and world number eight Li Na that she is in fact the world's top female tennis player.

"I think it's a true statement, without trying to sound full of myself or anything," Williams told reporters after overcoming Russian Sharapova 6-4 6-3 in the final of the season-ending tournament.

"I always said that if I'm playing well and I'm doing everything right it's really difficult to beat me. I still believe that."

Williams beat Sharapova each of the three times they met this year and also won all five of her matches against number one Azarenka of Belarus.

The American has ended the year with a 58-4 record and won seven titles but did not compete at two WTA mandatory events at Indian Wells and Beijing. Had she played the events she may have ended the year at number one.

"It's surprising to win two Grand Slams, the Olympics, Madrid and the Championships and to be number three," said Williams' coach Patrick Mouratoglou.

"If there is a bug somewhere, someone has to find it."

Williams said that her 2012 season comes a close second to her 2002 season, when she won three Grand Slam titles.

"I have to say number two only because I didn't win the Australian Open and French Open," she said.

"I faltered in the French and fell in the first round. I beat my record for 2002 match wise. But it's close. It's neck and neck."

Mouratoglou believes that if she stays healthy, the 31-year-old American can win many more majors.

Williams herself said it was possible she can again achieve what she did in 2002-2003, winning four straight majors, which she nicknamed the "Serena Slam".

"I could," she said. "I have a chance. Hopefully."