Roger Federer returns to number one as Novak Djokovic drops out of top 15

The Swiss becomes the oldest holder of the top spot in the modern era at 36 years and 279 days after Rafael Nadal dropped to second spot following his defeat to Dominic Thiem in the Madrid Masters quarter-finals on Friday.

Federer - who was number one for four weeks earlier this year - first held the number one position when he was 22 in February 2004, the longest gap between a player holding the game's top ranking. He has spent 309 weeks at the top of the ATP rankings.

The 20-times Grand Slam champion Federer is missing the clay-court swing, but is due to return on grass at the Mercedes Cup in Stuttgart on June 11.

Nadal drops down the rankings because he was defending a huge number of points won last year when he claimed titles in Monte Carlo, Barcelona, Madrid and the French Open meaning he had to emulate last season's success to defend his position.

Nadal can reclaim top spot before the grass-court season if he wins the Rome Masters this week and an 11th French Open, which begins on May 27 in Paris.

He will face Fernando Verdasco or Damir Dzumhur in his opening match in the last 32 at the Rome Masters.

Elsewhere in the rankings, former world number one Novak Djokovic has dropped out of the top 15 for the first time since January 2007.

His drop to 18th is his worst ranking since October 2006.

Having undergone elbow surgery after losing to Chung Hyeon in the Australian Open last 16 in January, the 12-times Grand Slam winner Djokovic has suffered a series of early defeats in his return to action with the last 16 in Monte Carlo his best run in five tournaments over the past three months.