He lost to Rafa in the US Open Final twice.

2010 he beat Federer in 5 sets to lose to Rafa in the final. The expected result as this was before his 2011 season and if you have to play two GOATs back to back you're gonna have a bad time.

2013

He played 5 sets against Wawrinka who then a few months later went on to win the Australian Open. He was again exhausted in the semis and went on to play a fellow Big 3 in the final.

Its not like Nadal is bad on hard court. Far from it! He is an amazing hard court player but if you're playing him with half a tank you're gonna lose. If Novak winning long 5 set matches is a great achievement its great BECAUSE its unexpected. The expected result is to be tired and lose.

Consequently, Rafa has been very fortunate that he has NEVER played Federer at the US Open. Not once in any round.

Given how Fed slaps Rafa on fast courts and hard courts I would be astonished if they played in the semi-finals and Rafa won.

In 2018 Novak had an easy draw and won easily.