Really good fighting from Gilles. He may have had no real first serve, but all the more reason why it was an impressive win. He basically won the match off of a second serve. He fought hard and didn't waiver during key moments where he could've been down 4-2 in the second set and defended many times a 0-40 hole. He also worked his magic and drew a lot of errors out of Youzhny with his defensive skills and basically being a human backboard.
Another fine effort from Gilles to make it as far as he can before facing someone who will obviously be tough to beat and the clear favorite now. Still, Gilles may frustrate Federer and have some chances the way he did against Murray, and there's no question that Gilles does tend to get motivated and up more for big marquee matches against the top guys.
Anyway, good job Gilles for turning things around with Youzhny after losing quite a bit to him. This makes three wins in a row over somebody he used to struggle with and who clearly is still playing some good tennis to have beaten Haas the day before. I have no doubt Gilles will try his best against Federer and hopefully it will be enough.