The winner arrived in the 11th minute as Robinson grabbed his first goal since arriving at Sixfields last season. Lee Nicholls’ long clearance was headed down by Henoc Mukendi and Robinson hit a dipping 30-yard volley over a stranded David Martin.
Louis Moult went close to doubling Northampton’s advantage when his shot just went the wrong side of the upright.
But the Dons hit back and created several good chances – Daniel Powell, Dean Bowditch, twice, Charlie MacDonald and Shaun Williams all failing to find the net.
The visitors picked up from where they left off after the break and it took a smart save from Nicholls to deny Stephen Gleeson before substitute Jabo Ibehre saw a header saved by Nicholls, although Cobblers sub Lewis Wilson should have made the game safe when he fired over after a quick break.
Ibehre missed a late opportunity when he failed to connect with MacDonald’s low cross from three yards as the visitors’ late pressure failed to produce an equaliser.