Federer, Nadal & Djokovic - Most Dissapointing Slam Loss

For Federer, Nadal & Djokovic getting to a slam final and not having to face each other is a great opportunity to add to their slam total. It doesn't happen often so to get there and find a fresh face across the net but to be unable to take advantage must be disappointing. I believe it has only happened 4 times. What loss represents the biggest lost opportunity and will be looked back on as the most disappointing?

Out of those only Federer's one strikes as particularly disappointing, in the context of a clear missed opportunity.

Nadal actually did well to win a set against Wawrinka given his circumstances, Djokovic was simply outplayed by a fantastic Murray in both those finals.
Fed's loss to Del Potro I think was a real missed opportunity, Del Potro played well but Federer had chances to put that match to bed.

The Fed loss to del Potro was, I think, the only time he's been two sets to one up in a GS final and lost. Should really have been 2-0 up in that match, too.
He had a great chance to win four slams in a row and would have (chucking in the 2010 AO) had he beaten del Po who was playing in his first, and so far only, GS final. Got to be a bad loss.

Best opportunity spurned was Federer v Del Potro in 09.

Worst performance was Djokovic v Murray at Wimbledon. He was 4-1 up in set 2 and 4-2 up in set 3 but didn't even get as far as a tie break in either.