Manchester City boss Manuel Pellegrini reckons star striker Sergio Aguero will run fierce rivals and neighbours Manchester United ragged in the derby.
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Last year's top two clash today in what will be the Chilean boss and new United chief, David Moyes' first Manchester derby.
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But Pellegrini believes it will be the Argentine, who has starred in previous encounters, who could prove the key man.
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He said: "Sergio is very important, he is an incredible player, he makes a difference in every game he plays.
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"He didn't do a very good pre-season because he has a lot of problems but now every game he is playing better.
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"I am sure he will play a very good game on Sunday because Sergio always appears in important games" Aguero settled the last clash between the two sides with a stunning solo effort at Old Trafford in April.
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And despite an injury hit pre-season the striker has appeared to hit form at just the right time as he scored one, created another and hit the post in City's 3-0 Champions League win over Viktoria Plzen.
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The win came as a welcome relieft to Pellegrini as City finally got their first win in Europe's elite competition after being knocked out at the group stage the past two seasons.
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"Yes it is important to win in the Champions League," the boss added.
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"There are no easy games. We saw a lot of games were very difficult for a lot of important teams so it was very important to start winning."
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City and United have both stuttered in their starts to the season and the City manager sees the game as crucial to both team's title aspirations but refused to say it is the be all and end all.
And he surely did. Manchester United did not just have any answer to all of Manchester City's questions tonight. Too sad....