>Last round of a US Open can be brutal (Think Mickleson and Montgomery both dbl bogey on the 18th several years ago)

Absolutely.
Tamar's right in wondering why some seemingly unbeatable teams fold at crucial moments.
It's a great question.
Golf's history is filled with unfathomable examples.
DJ's 3 putt from 12 feet last year on 18 at Chambers Bay is a cruel example.

Sam Snead, who in my estimation was the most talented golfer ever - and possibly the most talented athlete ever - blew several leads at US Opens and, while his record of winning over 80 events (all the more amazing since he spent 4 years in the army during WWII at his prime) still stands, he never won the US Open.

That's why DJ's birdie on 18 at Oakmont - one of the most brutal holes in the game- will rank with the best holes ever played in the history of the US Open.
He hit each shot perfectly when everything was on the line and disaster lay in waiting for even the smallest mistake.