Federer is having to muscle the ball too much. Long gone is the languid 'liquid whip' forehand; it's been replaced with one that often displays a small hitch, and is far more measured and manufactured. While Tsonga was finding ways to hit through the court, Roger by comparison was struggling. He always did rely on fluid, harmonious technique in order to generate his wicked pace and spins but with his more abbreviated stroke productions, which have slowly manifested themselves into his game over the last 5 years, he is unable to generate the same sort of consistent force - he cannot 'muscle' a ball in that manner in the same way that Tsonga can or indeed as proved recently, with his very strange and abbreviated swing mechanics indeed, Bernard Tomic.
In short, I don't think he'll find the adequate answers to hit through Murray, and certainly not Nole. He still has a chance though, can't count out silly old Wodgie now, can we.
"If you're gonna be 5'8'', you better not be bald, fat and drunk whilst asking to be put in the 'all-time great sportsman' conversation." - Zoid