New York - Novak Djokovic and Roger Federer meet for the 42nd time in Sunday's US Open final but forecasts of rain and thunderstorms threaten to make for a trying afternoon.
Top seed and world number one Djokovic, the 2011 champion and playing in his sixth New York final, is looking for a 10th major to pull level with American Bill Tilden.
Victory would also be his third Grand Slam triumph of 2015 after the Australian Open and Wimbledon, with only a final defeat to Stan Wawrinka at the French Open preventing him from contemplating a rare calendar Grand Slam on Sunday.
Djokovic, 28, trails Federer 21-20 in head-to-head meetings but leads 7-6 at the Slams, including the last two Wimbledon finals as well as their last two clashes in New York.
"I came here with a wish and a mission to reach the finals and fight for the trophy. So I got myself in that position," said Djokovic.
"It's already a great result. But I want to get that final step on Sunday and get my hands on that trophy.
"I'm used to all the expectations and pressure. It's part of what I do."
Federer, chasing a record sixth US Open title and 18th Grand Slam title, has been without a major since Wimbledon in 2012.
But he has been in inspired form at the US Open, dropping serve just twice in 82 service games and not having lost a set since the Wimbledon final.
The Swiss star was champion from 2004-2008 and runner-up to Juan Martin del Potro in 2009.
At 34, he is bidding to become the oldest champion in New York since 35-year-old Australian Ken Rosewall in 1970.
"Against Novak, I think it's just a straight shootout, and I think that's the cool thing about our rivalry. It's very athletic," said Federer playing in his 27th Grand Slam final.
Despite the anticipation, the weather looks set to have a major impact, one year out from the 23,000-capacity Arthur Ashe Stadium having its retractable roof up and running.
The New York weather forecast calls for a 50 percent chance of rain at the scheduled 4pm start time with scattered thunderstorms.
But the skies should clear as the day progresses indicating the match will finish Sunday, just later than planned.
Also overshadowing the occasion is Federer's controversial 'SABR' attack, his new tactic which sees him charge the second serve as the ball is being delivered, allowing him to chip it back and control the net.
Djokovic has dismissed the 'SABR' ('Sneak Attack By Roger') while his coach, Boris Becker, blasted it as disrespectful to opponents.
"If he would have played a John McEnroe, Jimmy Connors, Ivan Lendl or even me, we would have said 'Roger, in all honesty I like you but I'll go straight at you,'" Becker told Sky Sports.
"In my generation guys would not have accepted as it is now. It's almost disrespecting the other guy's serve."