As for Nadal, he's kind of in the same position with Almagro, a dangerous player, with explosive ground strokes, yet completely unsuccessful against the world #2. Just two weeks ago Almagro, won a set off Nadal in Madrid and it turned out to be the only set that Nadal lost, for the entire tournament. Yes, I think Almagro, has the game to trouble Nadal, but it remains to be seen if he's good enough to beat him. I'll go with Nadal to win this one in 4 as well.
The Berdych/Youzhny match is tough to call. The head-to-head between these two players is very tight but slightly favors Youzhny. Youzhny, is also the higher ranked player although Berdych, is in better form than years gone past. This could be a close competitive match.
Finally there's Djokovic vs Melzer and I have to take Djokovic, for this match. He's the higher ranked player, who's familiar with reaching the later rounds of the majors. The Austrian, Melzer, played a tremendous match in the fourth round to take care of Teimuraz Gabashvili in 4 sets. It was impressive but I don't think it's enough for him to beat the high ranked Serbian. I'm picking the Djoker, to win this in 4 sets.