After sharing the first three grand slam titles of the season, the US Open offers the chance for one of the dominant men's players to stamp his authority on 2018.
Roger Federer made the early running, winning his 20th slam crown in Australia and becoming the oldest man to be ranked world No.1.
However, Rafael Nadal wrestled control back on clay before Novak Djokovic discovered his form again to win Wimbledon.
Djokovic headed to New York fresh from beating Federer in Cincinnati to become the first player to complete a career Golden Masters - all nine ATP Masters 1000 titles - but the man who has proved hardest to beat this year is Nadal.
The Spaniard has lost only three matches all year and two since suffering a hip muscle injury in Australia which ruled him out for two months - he sits well clear of his rivals at the top of the rankings.
Nadal begins the defence of his US Open crown against compatriot David Ferrer on Monday feeling confident and fresh after winning the Rogers Cup in Canada two weeks ago.
"It has been a very positive season," he said.
"A fantastic clay-court season, then a very positive start in Toronto of the hard-court season playing a good event there.
"That's important for the feelings, for the confidence. That gave me a chance to rest the week after in Cincinnati."
Nadal is in the opposite half of the draw to Federer and Djokovic and is seeded to meet world No.3 Juan Martin del Potro in a repeat of last year's semi-final.
The Argentinian, the 2009 champion in New York, is at a career-high ranking and has reached at least the quarter-finals at three of the past four slams - Nadal has been the man to stop him each time.
For Del Potro, though, the most important thing is having finally moved past the wrist problems that left him fearing for his career.
"Sometimes I have to deal with pain in my wrist, which is normal after all my surgeries," the 29-year-old, who plays American Donald Young on Monday, said.
"But I think it's amazing for me just thinking about tennis, not talking any more about the injuries, and coming to this tournament thinking about my highest ranking or my big expectations."
