They have both been brilliant and their feeling of supremacy will start to grow and make them even better. You need to be lucky too and Ferdinand and Vidic are having a spell without injury which they didn't enjoy last season.
Case for the defence: Rio Ferdinandand Nemanja Vidic have been superb
They have already played together 14 times this season, four more than the whole of last season.
Not making Ferdinand captain and instead choosing Vidic is looking like a masterstroke from Sir Alex Ferguson. It put Rio's nose out of joint. So now he is making a point to the manager every time he puts in a great performance.
Ferguson barely ever praises Ferdinand but is always saying nice things about Vidic. That will annoy Rio but his boss is the one benefiting.
Rio is not flying forward any more like he did earlier in his career and has admitted he now prefers 'fighting fires'. He gets a lot of pleasure from his defensive blocks and headers while before he sometimes wanted to show too much trickery. The injuries he has had mean he has to manage his energy better, which means he is taking fewer risks.
I also noticed in United's last outing at Tottenham that Rio is demanding more from his team-mates than ever before, shouting at the people around him. I see a real hunger in his eyes now that he is not in his comfort zone any more - he needs to show Ferguson that he may not be captain, but he is still the best.
Respect: Former Arsenal team-mates Tony Adams and Martin Keown
Vidic does all the important things well. He heads the ball, attacks it and there are no questions over his positional sense. You would be amazed at the number of defenders who don't do those things.
They have different approaches to fouling: Rio has barely committed one all season but Vidic walks a fine line sometimes. You saw him pulling Rafael van der Vaart's shirt in the box last week but he was careful that he did it from an angle that the referee couldn't see. He is clever and will do anything to help his team.
In any partnership, you respect one another but you want to be top dog. It was like that with myself and Tony Adams. Vidic is the captain but Rio will think he is top dog. As a result of that, United benefit. Ferguson's ploy has got the best out of Vidic too.
I played 10 games the season we went unbeaten at Arsenal and, first and foremost, your focus is just on winning the league. Once you've done that, it actually becomes tougher to stay unbeaten as part of your motivation has gone.
If they do remain unbeaten, I don't think it will make them Ferguson's best ever side. Who is to say they would even definitely win the league? Looking back at my time at Arsenal, I think our teams of 1998 and 2002 were just as good as the 'Invincibles'.
Ferguson will just want to win the title.
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