Federer, Nadal at crossroads
Despite turning 34, Federer was an impressive winner of a seventh Cincinnati Masters title last weekend, seeing off world number one -- and US Open favourite -- Novak Djokovic in the final.
It was the Swiss star's 87th tour title and revenge for losing a second successive Wimbledon final to the Serb last month.
But Federer has stumbled badly in New York in recent years.
A five-time champion from 2004-2008, he was runner-up to Juan Martin del Potro in 2009 but hasn't been back to the final since.
His record at the Grand Slams in 2015 has also been mixed.
The seven-time Wimbledon champion may have at least reached the final at the All England Club, but that run was preceded by a shock third round exit to Italian journeyman Andreas Seppi at the Australian Open, his earliest in Melbourne in 14 years.
He then endured a quarter-final loss at Roland Garros to compatriot Stan Wawrinka.
Federer's last Grand Slam title came at Wimbledon in 2012 and if he wins the US Open this year, he would be the oldest champion since 35-year-old Ken Rosewall back in 1970.
"I haven't been in a final (in New York) since 2009. So I got my work cut out," said Federer, who was beaten by eventual champion Marin Cilic in the semi-finals last year.
In contrast to the Swiss player's staying power is Nadal's swift, brutal decline.
The 29-year-old Spaniard, the 2010 and 2013 champion in New York, has endured a tough year, the knee joints and wrists looking stiffer and weaker.
After being deposed as French Open champion -- his quarter-final loss to Djokovic was only his second ever defeat in Paris -- Nadal slumped to 10 in the world, his lowest ranking for a decade.
He has recovered to eight, but he is no longer the player that once struck terror into rivals.
Nadal has lost 14 times already this year compared to 11 in the whole of 2014, seven in 2013 and just six in 2012.
He sat out the 2012 and 2014 US Opens because of injury.
At Wimbledon, he was knocked out in the second round by Germany's Dustin Brown while his North American hardcourt season ended in a quarter-final loss to Kei Nishikori in Montreal and a third round exit against Feliciano Lopez in Cincinnati.
"I never consider myself a big, big star. So I appreciate when all the good things are happening to me," said Nadal.
"I am having a tough year, yes. Not a terrible year. I cannot make a drama about these kind of things. This is not the moment to cry."
Djokovic already has the Australian Open and Wimbledon titles under his belt in 2015, taking his majors total to nine.
The US Open champion in 2011, Djokovic was runner-up in 2012 and 2013 before suffering a shock semi-final loss to Nishikori 12 months ago.
The 28-year-old boasts a 56-5 record this year but two of those defeats have come this month -- to Andy Murray in the Montreal Masters final and then against Federer in Cincinnati.
He has also been troubled by an elbow injury.
"I played a couple good matches and couple not‑so‑good matches," said Djokovic, whose rolleroaster career at the majors has also seen him lose eight finals.
"The conditions in New York suit me a little bit better, so I look forward to it."
Murray, the world number three, won in New York in 2012, ending Britain's 76-year wait for a Grand Slam men's singles champion.
He has made at least the quarter-finals in New York in the last four years.
The 28-year-old could set a record for the largest payout in tennis history at the US Open -– $4.3 million.
That would be $3.3 million for winning the tournament and a $1 million bonus for winning the US Open Series title for performances in the hardcourt warm-up events.
Outside of the 'Big Four', Stan Wawrinka, the French Open champion, has made the semi-finals in New York on just one occasion in 10 visits.
Defending champion Cilic faces the task of proving he's not a one Slam wonder.
The 26-year-old world number nine only started his season in March after suffering a shoulder injury and has yet to make a final this year.
World number four Nishikori became the first Asian man to reach a Grand Slam final in New York last year.
But despite winning in Washington and making the semi-finals in Montreal, the 25-year-old Japanese was forced to skip Cincinnati with a left hip injury.
AFP