Have you been able to digest Manchester City’s shocking 6-1 win over Manchester United at Old Trafford? I haven’t.

As far as I’m concerned, United’s biggest home defeat since 1955 was one of the most unexpected scores in recent English Premier League history.

How did this happen? I have my theory and it involves Alex Ferguson tinkering with his line-up too often and the simple fact that some of United’s players are overrated.

Let’s start with point number one. There is no doubt that Fergie is one of the best managers of all time. I won’t dispute that.

His record speaks for itself and he has been able to keep United at the top for over two decades with his phenomenal ability to motivate and rejuvenate teams year after year.

However, he is human and humans make mistakes. I already thought that leaving Wayne Rooney and Nani out of the starting line-up for the previous week’s game against Liverpool was a mistake, and his continuing tinkering for the game against City backfired in a major way.

In my opinion, there is no way Jonny Evans and Danny Welbeck should have started on Sunday.

Evans is a mediocre player and, despite showing some signs of promise earlier in his career, hasn’t developed as I thought he would.

Phil Jones should have taken his spot in the center of defence. As far as Welbeck is concerned, he is a talented youngster but still hasn’t done enough to earn a starting place in a crucial derby against City. Javier Hernandez could and should have played up front.

Tactically Fergie also could have done better. He went with Anderson and Darren Fletcher in center of the park and they lost the midfield battle to Yaya Toure, Gareth Barry; Nani and Young were outplayed by the exceptional David Silva and James Milner.

United were eaten up by Barcelona in the Champions League final by playing only two men in the center, and it happened again on Sunday.

Tottenham had tried the same philosophy earlier this season and they were also thrashed at home by Roberto Mancini’s side.

A fluid 4-3-3 formation, which turns into 4-5-1 in defense, would have worked better for United and at least Ferguson would have had more numbers to combat City's industry in midfield.

Onto my thoughts on the players. I already told you what I think of Evans, but he is not the only United player who is overrated.

Darren Fletcher is a solid midfielder, but nothing more and nothing less. He is not a player that should still be at Old Trafford and in my view he wouldn’t get into the starting line-up of any of the top 10 teams in the world.

Why Ferguson insists on the likes of Fletcher and Michael Carrick baffles me. He will never win the Champions League again with either of those men in the side.

So, what’s next for United? Fergie has to go back to Plan A. Play your best players in your most important games. Rotate in the domestic cup competitions, but don’t experiment in crucial matches.

Oh, and while I’m at it, I would also suggest for the Red Devils to buy a top midfielder as soon as possible.

Wesley Sneijder has been linked and he would be a fantastic acquisition, but they also need someone strong and tough who can become a leader in the center of the park.

CNN Sport correspondent Pedro Pinto anchors CNN International’s coverage of the latest football events www.cnn.com/football