Rafael Nadal booked his semi-final spot at the Mexico Open by battling past Yoshihito Nishioka in straight sets, while top seed Novak Djokovic suffered another stunning exit in a shaky start to 2017.

World number one Andy Murray insisted Sunday that Novak Djokovic will remain his biggest threat in 2017, as the pair prepare for a potential first clash of the season in Doha this week.

Novak Djokovic, well rested after not playing since Monday, resumes his US Open title defence against fiery Russian Mikhail Youzhny, a two-time semi-finalist in New York.

Novak Djokovic opens defence of his U.S. Open title with a laboured 6-3 5-7 6-2 6-1 win over Poland's Jerzy Janowicz that brings new concerns about the world number one's fitness.

Novak Djokovic and Rafael Nadal get their US Open campaigns under way Monday in the shadow of Arthur Ashe Stadium's spectacular $150 million retractable roof and alongside rock music legend Phil Collins.

World number one Novak Djokovic has questioned equal prize money in tennis, suggesting men should get better awards as they have more spectators.

It was another epic struggle in a long list of hardcourt battles between the two top players in the world, who have met 38 times with Swiss great Federer still holding a slight 20-18 edge.