If someone had told Roger Federer 13 months ago that reclaiming the world number one ranking would require three more grand slam titles and three Masters 1000s, even he might have declared it mission impossible.
One of the most stunning late-career runs witnessed in any sport has seen Federer put together a sustained spell of brilliance few believed was possible when he missed half of the 2016 season with knee and back problems.
Incredibly Federer first became world number one in 2004 when he beat Juan Carlos Ferrero in the semi-final of the Australian Open before going on to take the title.
(Inputs from Reuters)