Fourteen-time Grand Slam winner Rafael Nadal has dropped to 10th in the latest world rankings - his lowest position in more than a decade.
The Spaniard, 29, has fallen after losing to world number one Novak Djokovic in the French Open quarter-finals last week.
It is Nadal's lowest ranking since he was 11th as a teenager in April 2005.
Swiss Stan Wawrinka, who beat Djokovic to the Roland Garros men's singles title on Sunday, climbs to fourth.
"I must improve my level of tennis, my intensity on the court," Nadal said on Monday. "If I can do that I'm confident that I can return to my best level."
Djokovic, 28, stays ahead of Switzerland's Roger Federer and Britain's Andy Murray, who was beaten by the Serb in the last four.
Serena Williams, who claimed her 20th Grand Slam singles' title, increased her margin at the top of the women's rankings.
The 33-year-old American's nearest rival is Czech Petra Kvitova, who has risen from fourth.
Russian Maria Sharapova, 28, drops two places to fourth following her fourth-round loss to eventual finalist Lucie Safarova, 28, with the Czech player moving to a career-best seventh.
British number two Kyle Edmund, 20, is up to his highest ranking of 101 after he beat French veteran Stephane Robert in the first round of the French Open, before he pulled out of the tournament with a stomach injury.