Mwaruwari fired home the simplest of chances from Sulley Muntari´s left-wing cross in the 81st minute and four minutes later Johnson hit a low effort past Chris Kirkland from the edge of the box to make it 2-0.
Wigan had their best chance after just two minutes when Paul Scharner hit the post with a diving header but boss Chris Hutchings will be concerned that his side have now gone more than five hours without a goal.
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