Alan Lee grabbed a brace for Rotherham, including the winner in the 87th minute whilst Steven Reid (pictured) scored twice for the visitors.
Walsall remained top with a 2-1 home win over Port Vale, Pedro Matias put the home side ahead in the 35th minute and Dean Keates slammed home a penalty in the 50th minute to make it two.
George O'Callaghan's goal in the 78th minute ensured a barmstorming finish but The Saddlers held out to remain top by a point.
Wigan were held 2-2 at home by Brentford but remain in fourth, whilst Bristol City climbed into a playoff place with a 4-1 home thumping of Bury.
At the bottom it was heartbreak for Oxford as they lost 3-2 to Oldham Athletic.
Mark Innes' own goal gave the visitors hope but a minute later Paul Jones fired in the winner to give Oldham the win.
Luton are now seven points clear of Oxford after a 3-1 home win over Stoke who looked as though they were still suffering from the hangover sustained after their 8-0 midweek mauling at the hands of Liverpool.
Click on the result for the relevant report:
Brentford 2 Wigan Athletic 2
Bristol City 4 Bury 1
Colchester United 2 Notts County 0
Northampton Town 0 Swindon Town 1
Oldham Athletic 3 Oxford United 2
Peterborough United 1 Wrexham 0
Reading 3 Cambridge United 0
Rotherham United 3 Millwall 2
Stoke City 1 Luton Town 3
Swansea City 0 Bristol Rovers 0
Walsall 2 Port Vale 1
Wycombe 0 Bournemouth 3
