WTA rankings: Caroline Wozniacki plunges to six-year low

Caroline Wozniacki has fallen to No. 18 in the WTA rankings. (Jeff Gross/Getty Images)

Former No. 1 Caroline Wozniacki tumbled to 18th in this week's WTA Tour rankings, her lowest position since 2008.

The 23-year-old Dane's six-spot drop came after she lost to Jelena Jankovic 6-3, 6-1 in the fourth round of the BNP Paribas Open, where Wozniacki was defending finalist points from last year. Wozniacki fell to 8-5 in 2014, with her best result a semifinal appearance at the Dubai Championships.

Also last week, Wozniacki -- the year-end No. 1 in 2010 and '11 -- reportedly split with her second coach since January. A Danish newspaper reported that she is no longer working with Michael Mortensen, who joined her team after Wozniacki parted ways with Thomas Hogstedt following a three-month stint.

Wozniacki has a first-round bye at this week's Sony Open. She will play either Monica Puig or Magdalena Rybarikova in the second round.

In other rankings news to emerge from the Premier Mandatory tournament at Indian Wells:

• Simona Halep, as noted earlier, climbed to No. 5, the highest position ever for a Romanian woman.

• Maria Sharapova fell from fifth to seventh, her lowest spot in three years.

• Jelena Jankovic rose from eighth to sixth, her highest spot in three years.