Rafael Nadal's return to the top of the world rankings is "as impressive as any" of the 15-time Grand Slam winner's achievements, says men's tennis chief Chris Kermode.
The Spaniard, 31, replaced Britain's Andy Murray as world number one on Monday - the first time since July 2014 he has held top spot.
It comes despite dealing with a series of knee and wrist injuries since first holding top ranking in 2008.
"It is unprecedented," said Kermode.
"Rafa has been setting records throughout his remarkable career and this one is as impressive as any. It shows incredible dedication and longevity," the ATP president added.
Nadal's recent rise has been helped by injuries to rivals such as Murray, who is recovering from a hip problem.
A back injury for 19-time Grand Slam winner Roger Federer and an elbow problem for 12-time Slam winner Novak Djokovic have similarly helped him in his rise.
And Nadal, who previously spent 141 weeks as world number one, said: "Being number one after all the things that I have been going through the last couple of years is something unbelievable."
He later told fans on social media: "Today is a special day, going back to number one, I'm very happy."