Police praised the un-named worker as they released CCTV of the raid showing him confronting the hooded, knife-wielding thieves.
Despite being outnumbered and stabbed in the arm, he whips his shoe off and forces them back towards the door of the service station.
The robbers eventually flee empty handed - being chased onto the forecourt by the worker wearing only one shoe.
Police hope the CCTV will prompt information about the raid, at around 1.20am on Saturday at Mercury Service Station on Manchester Road in Westhoughton, Greater Manchester.
Detectives are appealing for help to trace the woman who walks into the store seconds before the incident.
The victim, who also picked up a glass jar to defend himself during the attack, suffered two puncture wounds to his arm and later needed 12 stitches.
Detective Constable Malcolm Cheetham from Greater Manchester Police (GMP) said: "This man's heroic actions meant that these thieves were able to get away empty handed, but for his trouble he was wounded.
"We are appealing for witnesses but in particular we need to hear from the woman who walked in only moments before but didn't stick around to give the police her account - probably because she was so shaken up.
"We need to find out everything that she may have heard or seen, including before the robbery. We urge her to get in touch as soon as possible."
Both of the offenders were black men. The man with the knife was about 6ft tall, of medium build and in his early to mid 20s. His accomplice was about 5ft 9in tall and of medium build.
Anyone with any information is asked to call police on 0161 856 1527 or call the independent charity Crimestoppers anonymously on 0800 555 111.