The umbrella broke while Joseph Dolan (22) was hitting the man on the face with the hooked end of it, Dundalk Circuit Court was told.
It was the first of two robberies he carried out in a 10- hour period and at the time he was on bail for another offence, the court heard.
Dolan, of no fixed abode, admitted robbing Pat 'Sonny' Murphy on Poorhouse Lane, Drogheda, as he walked home after 7pm Mass on March 11 last year.
Mr Murphy has no memory of the incident but when he arrived home at 8.10pm he told his wife he had been beaten and robbed, he had blood on his face and jacket and a swollen eye.
His son John was contacted and made his way to the house via the same lane where he found his father's broken umbrella on the ground.
He also noticed blood on the footpath, the court heard.
The court heard that before Mass -- in St Mary's Church, Drogheda -- Dolan had been given €50 from the priest after telling him he needed money for food and accommodation.
Mr Murphy was treated at Our Lady of Lourdes Hospital and needed five stitches to his eyebrow and his eye was closed for three days.
He also suffered an injury to his ear and his fingers.
Gardai found Mr Murphy's blood-stained Mass leaflets, tissues and glove on the laneway and his DNA and that of Dolan were both found on the umbrella when it was forensically examined.
When arrested by gardai Dolan said he had given Mr Murphy a box to the side of the face after which he fell to the ground. He then hit him with the hooked end of the umbrella two to three times.
"He broke the umbrella when he was beating him," the garda said. He had, the court heard, told gardai that he had hit him "as hard as he could".
Mr Murphy had keys to his house and car taken as well as his wallet.
At 5.30am the following morning Dolan had with a teenage girl got a taxi from Peter Street, Drogheda, to the nearby Mellifont Park.
When it stopped Dolan held the taxi driver's head against the driver's headrest and used his other hand to hold a weapon, described as a steak knife, against his throat.
He told him he would slit his throat and when the driver struggled he stabbed him a number of times in the shoulder, head and back.
The driver pretended to pick up something and said to him "well now who will stab who?" and he called for assistance on his taxi radio.
The pair ran off and he realised his iPhone had been taken.
When the pair were arrested at a squat in Drogheda the following day, gardai recovered the blood-stained ¤50 note given to Dolan by the priest. Dolan has 27 previous convictions.
Passing sentence Judge Leonie Reynolds said it was a "savage beating" with an umbrella and the photos of the injuries, "are particularly distressing having regard to his advanced years".
She imposed three years for each robbery, to run concurrently, and suspended the final 18 months.
The sentence will start at the conclusion of a three year sentence he is currently serving for violent disorder.
Mr Murphy was not in court yesterday and told the garda he did not want to give evidence at the sentence hearing.