LONDON — Dinara Safina officially took over the top ranking on the WTA Tour on Monday, making her and older sibling Marat Safin the only brother-sister duo to have been No. 1 in professional tennis.

Safina, who has yet to win a Grand Slam title but twice reached a major final, is the 19th woman to top the rankings since they were introduced in 1975. She is also only the second Russian woman after Maria Sharapova to reach No. 1.

Safina replaced Serena Williams at the top, even though the American beat her in the Australian Open final this year. Last year, Safina lost to Ana Ivanovic in the French Open final.

Marat Safin was ranked No. 1 on the men's tour in 2000, the same year he won the first of two Grand Slam singles titles.

"He has two Grand Slams," Safina said of her brother in a video posted on the WTA's Web site. "He's still much better than me, so I have to catch him."

Safina won four titles last year.