Essien is a big addition for Milan, who seem to have been rejuvenated by new coach Clarence Seedorf after a dismal start to the season under Massimiliano Allegri.
Any hopes of the Scudetto died out in 2013 and even a magnificent 2014 won't guarantee European football for the Diavolo.
However, a 1-0 win over Hellas Verona on Seedorf's coaching debut and a remarkable comeback from 1-0 down with four minutes remaining to beat Cagliari 2-1 have brightened the mood.
The arrival of Essien will have further lifted spirits and will be a vindication for the player, who reacted angrily to reports in the Italian media that he had failed his medical.
Essien thanked his former colleagues at Chelsea on his Twitter profile as he left the club: "A big good luck to everyone at Chelsea", he said.
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