The thief brazenly walked into the 84-year old man's home while he was cutting the grass.
The elderly man suffered an eye injury after he and a neighbour battled to restrain him.
However, the intruder managed to break free and fled with the elderly man's wallet.
Police have described the incident as "sickening". The pensioner is still too traumatised to speak publicly about his ordeal.
His neighbour spotted the thief going into his house in Thornliebank, East Renfrew-shire, at around 1pm on Friday afternoon.
The pair went into the house and began searching for the intruder.
When they confronted him, they tried to stop him leaving and a struggle ensued. The 84-year-old suffered a bad cut to his eye.
The thief fled from the house in Woodfarm and was last seen in High Park heading towards Main Street in Thornliebank.
The pensioner was taken to the Victoria Infirmary where he had stitches put in an eye injury.
The suspect was in his 20s and around 6ft tall with a slim build. He was wearing a light-coloured jacket and light blue jeans.
Detective Constable Justine Murray said: "This was a sickening experience for an elderly man who bravely tried to capture the sneak-in thief.
"Unfortunately, he has been left not only traumatised but also with a nasty injury to his upper eyelid.
"I'd like to speak to anyone who was in the Woodside Avenue vicinity on Friday around lunchtime and may have seen the suspect hanging around the area."