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.