Tom Eaves scored against his former club but Harry Gray and Emmanuel Adegboyega were both left unmarked to head in and turn the game around. Here are our player ratings from a damaging defeat in South Yorkshire...
1. Ross Fitzsimons
Off his line smartly to spare McCarthy's blushes in the first half and then saved well with his legs in the second at 1-1. Badly let down by his defenders for both goals... 6.5 Photo: Pete Norton
2. Jordan Willis
No blame can really be laid at his door for this one. Other than Gray's equaliser - which he wasn't at fault for - Cobblers kept Rotherham relatively quiet for the 71 minutes he was on the pitch... 6 Photo: Pete Norton
3. Jon Guthrie
Battled valiantly in a losing cause as those around him wilted. Made so many clearances and won so many headers to keep Rotherham at bay in the final 30 minutes but it all proved in vain. Excellent flick to claim an assist for Eaves' first half goal. Frustratingly Adegboyega got the wrong side of him to head in the winner... 7 Photo: Pete Norton
4. Conor McCarthy
Made a decent early block but he was loose with some of his passing and got away with one poor clearance, saved by Fitzsimons. Headed not far wide shortly before Eaves struck and then helpless to prevent Rotherham turning it around... 5 Photo: Pete Norton