Maria Sharapova is back on top of the world rankings after a four-year break.
The new French Open champion last sat atop the WTA list in June 2008 but soon after required shoulder surgery which saw her ranking slump to 126.
The Russian, who first reached the summit in August 2005, usurps Victoria Azarenka, who had held the top ranking since her Australian Open victory in January.
However, Azarenka's fourth-round defeat in Paris enabled Sharapova to take over as number one by reaching the final, which she duly did.
"It's such an amazing feeling to be back in the position of being number one in the world," said Sharapova, who beat Sara Errani in Saturday's Roland Garros final.
"I had the joy of holding the number one trophy many years ago.
"Since then, I've gone through the injury and come back, and to be holding it a few years later is a huge achievement for me. It's a special day and I hope I can keep the ranking for a long time."
The longest period she has previously held top spot for is just seven weeks.
WTA chairman Stacy Allaster hailed the 25-year-old's achievement.
"Maria has once again proven what an extraordinary champion and fighter she is in regaining the WTA world number one ranking," she said.
"Her will to win and ability to overcome obstacles has made her one of the game's great ambassadors, an inspirational icon and a one of the world's most popular athletes."
It is Sharapova's fifth spell as world number one and this will be her 18th week in the position in total.
Sharapova proved herself the top player on clay over the past two months, winning titles in Stuttgart and Rome, as well as Roland Garros.
By winning in Paris, she became just the 10th woman to achieve a career Grand Slam, the sixth in the Open era.
She also won Wimbledon in 2004, the US Open in 2006 and the Australian Open in 2008.
Meanwhile, Errani made her top-10 ranking debut when the new WTA list was published on Monday.
The Italian climbs 14 places following her surprise run to the final.