Coventry and Sunderland have taken the last available playoff places after a dramatic final afternoon in the Championship.
Millwall were 3-1 up at half-time at home to Blackburn, and looked good for a playoff spot but wound up losing 4-3.
Sunderland snatched sixth place courtesy of a 3-nil win at Preston.
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Coventry held on for a 1-1 draw at Middlesbrough to finish fifth.
Northampton have won promotion from League Two after a 1-nil victory on the final day of the regular season at Tranmere.
They pipped Stockport - who were held to a 1-all draw with Hartlepool - to third place.
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Carlisle, Bradford and Salford are the other teams to make the play-offs, while Mansfield miss out on goal difference.
