I have noticed that Anderson rarely ever plays well when paired with Fletcher in a 442, he plays better with Carrick or Cleverly the only time he has a decent game with Fletcher is in a 433 formation. Probably has a lot to do with knowing his role within the team. When he plays with Carrick, Carrick always sits in front of the back four giving Anderson the freedom to roam and with Cleverly, they seem to have built up an understanding to share the attacking and defensive duties and it works very well but with Fletcher its almost like he is unsure of his role because Fletcher is always moving about and almost always leaving Anderson with the defensive duties even though Anderson dictates play a lot better than Fletcher in a 442. One game that always comes to mind is the carling cup game at upton park last year when west ham won 4-0 and the midfield of Anderson and Fletcher was all over the place and i would have thought SAF would have noticed this but obviously he knows better. For me, Fletcher is a much better player in a 433 because he is industrious and breaks up play a lot but he offers no creativity or invention in a 442, plus he is still not up to speed since his virus as he has been totally outshone by the likes of Petrucci and Pogba when they have played together in the reserves
They are both box to box type players so playing them together is never going to work unless as you say it is in a 4-3-3/4-5-1 (whatever you want to call it).
I was expecting Carrick to start with Anderson, so the team would be a little more solid, as we usually are against Chelsea. Maybe Fergie decided to go for more mobility in the centre. It worked thanks to some woeful finishing and defending on Chelseas part. But it doesn't matter who Anderson's partner is, he should not be giving the ball away as much as he did during that game with some wayward passing. But that said it made for a very entertaining and open game.