Although Sampras had 13 Slams under his belt in 2002, he didn't win any tournament since Wimbledon 2000. I considered he's a dark horse that year.
Sampras did not play well all year but nobody could be surprised when Pete started rolling so he wasn't a TRUE darkhorse. Sampras in 1990, however, is a different story. He was a true darkhorse then.
Orantes was the #3 seed when he won it and was a darkhorse only in the sense that Connors was unstoppable that year. He really roughed Connors up in the final
Newcombe in 1973 was the 10th seed.