There were four female members of staff working when 26-year-old Garry Tyrell held up the Gilbert Grocers store in Ridgeway, East Herringthorpe, Rotherham at around 10.25am March 10 this year.
Sheffield Crown Court was told how the 62-year-old woman working behind the till was first alerted to the robbery when she heard her colleague scream.
"She looked up and saw the defendant holding a knife in his hand, standing two feet away. The CCTV footage shows the defendant had his hood up and the knife was a long kitchen knife," said Louise Gallagher, prosecuting.
Ms Gallagher added that a witness to the robbery told police how Tyrell was only a few inches away from the shop worker and was holding the knife level with her face.
Tyrell demanded money from the shop worker behind the till, and she handed over £110 to him as soon as she was able to.
CCTV footage played in court showed how a member of the public ran at him with a trolley, him against a display unit.
The courageous man was assisted by two other men in the store who helped to take the knife from Tyrell and restrained him until police arrived to arrest him a short time later.
The money stolen by Tyrell was recovered by officers.
In a victim impact statement taken from Tyrell's 62-year-old victim on the day of the robbery, the woman said she truly believed Tyrell was capable of causing her really serious harm if she had not complied with his requests.
"Every time I close my eyes I see the man holding a knife," said the woman, adding: "I love my work and it's a type of escape from my worries. This has left me feeling scared. I don't see how I can return to work."
Tyrell pleaded guilty to one count of robbery and one count of having an article with a blade or point at an earlier hearing.
Judge Michael Slater said he wanted to adjourn the sentencing until Friday, to allow an updated statement to be taken from Tyrell's victim on how the robbery has affected her.
Tyrell's barrister is also due to mitigate on his behalf during Friday's hearing.