Match ends, Northampton Town 0, Rochdale 3.
Rochdale went top of League Two after they cruised to victory at Northampton, despite playing with 10 men for much of the second half.
Former Cobblers midfielder Ian Henderson gave the visitors an early lead with a low drive from close range.
Matt Lund then doubled Dale's lead on 54 minutes, but was shown a second yellow card for his goal celebration.
The hosts could not find a response, going three down when Joe Bunney met Henderson's pass to fire home.
Northampton remain 23rd, but are now three points adrift of safety, while Rochdale take over on top by a point from Chesterfield.
Northampton Town manager Chris Wilder told BBC Radio Northampton:
"We're big enough to stand up and say it wasn't good enough.
"Thankfully it's only three points lost, although, obviously, our goal difference has taken a battering.
"The players know that the managerial staff aren't happy and they shouldn't be happy on a personal level - both individually and collectively.
"People thought I was crazy coming here but I said we'd stay up when I arrived and I still believe that."
Rochdale manager Keith Hill told BBC Radio Manchester:
"We were ruthless. We could have scored more because we had other opportunities.
"I'm pleased with where we are and what we're doing - it's been a very good season so far and we've got nine games left.
"The league table doesn't lie but it's not really a concern.
"If we're in the same position with three games to go, we can start dreaming."
- 2McSweeneyBooked at 66mins
- 29RobertsonSubstituted forToneyat 78'minutes
- 34RavenhillBooked at 48mins
- 23DiamondSubstituted forDickensonat 45'minutes
- 18ConnellSubstituted forLópez Santamariaat 61'minutes
- 10López Santamaria
- 12LundBooked at 55mins
- 39BunneySubstituted forDonnellyat 77'minutesBooked at 81mins
- Mark Heywood
- Shots on Target
Second Half ends, Northampton Town 0, Rochdale 3.
Attempt saved. Leon McSweeney (Northampton Town) right footed shot from outside the box is saved in the top left corner.
Peter Vincenti (Rochdale) hits the left post with a right footed shot from the right side of the box.
Corner, Rochdale. Conceded by Ian Morris.
Peter Vincenti (Rochdale) wins a free kick in the defensive half.
Foul by Ian Morris (Northampton Town).
Joseph Rafferty (Rochdale) wins a free kick on the left wing.
Foul by Brennan Dickenson (Northampton Town).
Jack O'Connell (Rochdale) wins a free kick in the attacking half.
Foul by Cristian (Northampton Town).
Attempt missed. Ian Henderson (Rochdale) right footed shot from the left side of the box is close, but misses the top right corner.
Matt Done (Rochdale) wins a free kick on the right wing.
Foul by Chris Hackett (Northampton Town).
Attempt blocked. Cristian (Northampton Town) right footed shot from the centre of the box is blocked.
George Donnelly (Rochdale) is shown the yellow card.
Substitution, Northampton Town. Ivan Toney replaces Gregor Robertson.
Substitution, Rochdale. George Donnelly replaces Joe Bunney.
Attempt missed. Darren Carter (Northampton Town) left footed shot from outside the box misses to the left.
Joe Bunney (Rochdale) wins a free kick in the attacking half.