Rugby union: Northampton 31 Leeds Carnegie 24
They led 24-3 after 18 minutes after tries from Hendre Fourie, Rhys Oakley and Pete Wackett.
But the Saints were ahead by 54 minutes as their experienced England players turned the screw.
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Hide AdLeeds earned a losing bonus but finish level on points with Newcastle, but with a poorer points difference.
Their relegation will not be confirmed until May 18 and the outcome of the Championship play-off final.
If Worcester win they will be promoted and Leeds relegated.
But if Cornish Pirates win the Yorkshire club will be reprieved and the Premiership status quo will remain.