There is one over-riding reason why Manchester United let Carlos Tevez leave last summer, it can be found in the remarkably frank self-analysis that the Argentina forward offered while on international duty midway through last season.
Tevez's move to United should have lit the touchpaper of his career when he left West Ham in 2007. Oddly, he seemed to lose his spark. In the space of two seasons a magical, gifted attacking player was dumbed down to a willing, able but apparently limited workhorse.
Flying: Tevez celebrates scoring his second for City against Blackburn
Next week in the Carling Cup at Eastlands, United may find to their cost that since the player's move across Manchester to neighbouring City, Tevez's world has turned full circle again. A hat-trick in the 4-1 demolition of Blackburn on Monday night said everything about the roll that he is on.
Fifteen goals in all competitions for the season - just one fewer than United's Wayne Rooney - have included a run of 11 in his last nine games. With his confidence back, they are flying in from everywhere.
On Monday, there were two stunning efforts from distance and one that seemed to bobble in off his right thigh.
After the one-sided match which lifted City into fourth position, team-mate Nigel de Jong said: 'Tevez is on fire at the moment and I hope he will continue that for the rest of the season
'He is so important to us. He gets his rewards in goals but he makes other players better as well.
'He is an example to everyone in the squad, guys who were written off and younger players, too.'
My ball: Tevez walks off with the match ball after scoring three goals against Blackburn
The intriguing rivalry that now has Manchester so steamed up will be at the forefront of the nation's thoughts again next Tuesday when City and United meet in the semi-final first leg of the Carling Cup. As United have bristled at City's renewed threat in recent months, Tevez has found himself at the centre of it all.
The 25-year-old chose City in the summer after United failed to make good promises of a permanent contract they had talked about when he joined them from West Ham. In short, over two years, manager Sir Alex Ferguson decided he was not worth the £25million they had initially agreed to pay.
City sources told Sportsmail that when Tevez arrived at Eastlands he was a player who had lost his way a little.
It would appear, though, that the answer was very simple.
'Carlos is a good lad with a huge heart and enormous strength of character,' said the source.
Handful: Carlos Tevez tangles with Blackburn's Chris Samba
'But it's hard to get him to train at a match tempo. So if he isn't playing regularly in real games, then he loses his sharpness. I think that's what happened at United and that's what we have had to try to address.
'At the start of the season he had problems with his back and his ankle but we needed him so we pushed him into games and he did a job for the club.
'But all those matches have really paid off in the last couple of months as he has just got sharper and sharper.
STATS THAT SHOW FERGIE GOT IT WRONG SIR ALEX Ferguson may regret not putting more faith in Carlos Tevez. Often used as a impact substitute at Old Trafford, the Argentina forward has proved at Manchester City that if he starts a Premier League match, he will score goals.
West Ham(2006-2007)Appearances: 26 Starts: 19Substitute: 7 Goals: 7Goals from starting: 7Goals from sub: 0Mins Per goal when starting: 211
Man Utd(2007-2008)Appearances: 34Starts: 31 Substitute: 3Goals: 14Goals from starting: 14Goals from sub: 0Mins Per goal when starting: 187Mins Per goal from bench: 0
Man Utd(2008-2009)Appearances: 29Starts: 18Substitute: 11Goals: 4Goals from starting: 3Goals from sub: 1Mins Per goal when starting: 377.5Mins Per goal from bench: 349
Man City(2009-2010)Appearances: 19Starts: 17Substitute: 2Goals: 12Goals from starting: 12Goals from sub: 0Mins Per goal when starting: 122Mins Per goal from bench: 0
'He will still do his own thing. He will still have a bottle of Coke or a Mars Bar occasionally! But it's fine because of all the work he is getting through in matches.
'When we spoke to him about coming he just wanted to know if he would play regular games and if he would be at the heart of what we were doing. In some ways, he just wanted to be loved again.
'I think he had forgotten the type of player he once was and felt he needed a way to get that back.'
Tevez's success in the Barclays Premier League this season has been such that only two players - Cesc Fabregas of Arsenal and Chelsea's Didier Drogba - have actually been involved in more goals. So far, he has contributed 12 league goals of his own and provided five assists.
Previously in his career, he has been similarly effective. In Brazil, for example, Tevez scored at a rate of a goal every one-and-a-half games for Corinthians, while for Boca Juniors - when he was still a teenager - he scored a goal every three matches.
At United, of course, his output in terms of goals was relatively low - he scored 18 goals in 63 appearances - and it was this return that prompted manager Ferguson to suggest last summer he was not worth the money. De Jong added: 'Some people have a different view on Carlos but if they look at him now, they will change their mind.
'I'm just glad he's playing for us.
'There are a lot of great players in the Premier League but you look at his impact the last few weeks.
'There is a reason he was voted Player of the Month for December. At this moment he is maybe the best striker in the Premier League.'
When United faced City in the league in September, Tevez was still adorning controversial posters in the centre of Manchester. They have gone now but the real Tevez has since arrived.
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