fed took a mental vacation in that match and managed to let it get away from him. tsonga is not 1/4 the player fed is.
this is not new. nadal did the same thing after going up 4-2, 30-15 in the 5th at the australian open. he either took a mental vacation thinking the match was a done deal or he started thinking too damn much.
tennis is an instinctive sport. it is not rocket science. you work to put yourself in a winning position and then you finish it.