Shaun Wright-Phillips, lively in the opening stages of the match, was forced from the field with a hamstring injury and from that point onwards matters quickly deteriorated for the home side.
Forest took the lead when England international Richards failed to deal with a routine long ball, allowing Tyson space to score in spectacular style before Earnshaw added to City's woes.
City were without their Brazilian playmaker Robinho and the injured Stephen Ireland, but nevertheless fielded a strong side which was unsurprisingly greeted to a cacophony off boos as they made their way down the tunnel at the break.
Daniel Sturridge, the catalyst of City's magnificent comeback at Blackburn last week, had a couple of efforts on goal, the best of which was a lofted shot as Paul Smith advanced.
And Jo would probably have pulled a goal back if Wes Morgan had not made a brave block 20 minutes from the end.
However, City's missed chances were all made irrelevant when substitute Hamann failed to spot Garner lurking as he tried to find Richard Dunne with a throw-in and the young midfielder gleefully drove home.
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