Scipio was elected consul and appointed to sole command in Africa; usually theatres were allocated to the two consuls by lot. He was granted the usual right to conscript enough men to make up the numbers of the forces there and the unusual entitlement to enrol volunteers.

Scipio moved the Romans' main camp back to near Carthage, closely observed by a Carthaginian detachment of 8,000. He made a speech demanding tighter discipline and dismissed those soldiers he considered ill-disciplined or poorly motivated. He then led a successful night attack and broke into the city with 4,000 men. Panicked in the dark, the Carthaginian defenders, after an initial fierce resistance, fled. Scipio decided that his position would be indefensible once the Carthaginians reorganised themselves in daylight, and so withdrew. Hasdrubal, horrified at the way the Carthaginian defences had collapsed, had Roman prisoners tortured to death on the walls, in sight of the Roman army. He was reinforcing the will to resist in the Carthaginian citizens; from this point there could be no possibility of negotiation or even surrender. Some members of the city council denounced his actions and Hasdrubal had them too put to death and took full control of the city.

The renewed close siege cut off landward entry to the city, but a tight seaward interdiction was all but impossible with the naval technology of the time. Frustrated at the amount of food being shipped into the city, Scipio built an immense mole to cut off access to the harbour via blockade runners. The Carthaginians responded by cutting a new channel from their harbour to the sea. They had built a new fleet and once the channel was complete the Carthaginians sailed out, taking the Romans by surprise.