Madhavan Rama was alone when the raider burst into AJ’s Convenience Store in Paulsgrove.
CCTV footage shows how the attacker confronted Mr Rama at the Cheltenham Road shop and grabbed him by the throat.
He was then repeatedly punched after trying to restrain the robber, who shouted demands for cash while wielding a blade.
Dressed head-to-toe in black and with a hood covering his face, the attacker fled empty-handed after the botched raid on Saturday at 4.25pm.
Mr Rama has been left with a bruised nose and neck after being punched, throttled and pushed to the floor.
He told The News: ‘I was shocked as the attack was unexpected.
‘I was bent down arranging the cigarettes when the man rushed towards the till and punched me in the nose.
‘When I saw the knife, I got nervous and tried to hold his hand so he couldn’t stab me, then he grabbed my neck.
‘I tried to push him back, but he kept hurting my neck.
‘I kept fighting back until he heard someone coming in and ran out.
‘I felt shocked and shaken up by the attack as it was unexpected in a busy residential area.’
Police have said they are looking for the attacker and a woman, seen on CCTV outside the shop, in connection with the incident.
Shop owner Rama Samy said: ‘My colleague was here alone.
‘The man came behind the counter with a knife asking for money.
‘My colleague struggled to push him over because he had a knife in his right hand.
‘He was scared and panicking, he didn’t know what he was going to do.
‘He pushed him over and they were both at each other.
‘The guy leapt over the counter to try to open the till.
‘Mr Rama has got bruising to his nose and neck.’
The CCTV footage obtained by The News shows stunned customers outside the shop concerned about what is taking place inside.
Shoppers were yesterday streaming into the store asking after Mr Rama, who they have hailed as a hero.
Detectives at Hampshire police have launched a probe into the attempted robbery.
Mr Samy has had the shop for seven years.
He said: ‘Sometimes we’ve had anti-social behaviour and abuse, but this is more serious.’
The raid happened between 4.25pm and 4.35pm.
A police spokesman said: ‘A man with a knife demanded money from the shopkeeper.
‘An altercation followed and the shopkeeper was assaulted.
‘The suspect left without any money.
‘Investigations are ongoing.’
Anyone with information should call detectives at Hampshire police quoting 44170082323.