Two of the greatest clutch players in recent times. However I feel that they are both clutch in a different way. Sampras was an excellent front runner. Once he went up a break, it was pretty much game over for that set. His serving would go into GOD mode ( 15-0 ace, 30-0 ace, 40-0 strong serve overhead smash, game). I can't remember many occasions where Sampras has lost after being significantly ahead. Once Sampras god a whiff of blood, you were in BIGG trouble. However if you could get a lead over Sampras, then he became less clutch. Nadal on the other hand is not necessarily an excellent front runner. Of course he is a good front runner, but not an excellent one like Sampras. If Nadal were 2 sets up vs a top player like Fed, Djo,Murray etc I would still give them a shot (except on clay). But where Nadal is tremendous is at coming from behind and playing every single point like it were the last point. You could be 5-0 30-0 up and if you played 10 % less than your best, Nadal would make you pay for it. If i had to put my money on someone to close out a match , it would be Sampras. If i had to put my money on somebody to make a comeback from a bad position , it would be Nadal. That's why a Sampras vs Nadal match would be a great battle even at the mental level. Clutch vs Clutch at its best.