The pensioner was assaulted after being pursued from a bus stop in Harcourt Street, Dundee, at 1.30pm on Wednesday.
The attacker made off with a four-figure sum of cash, police said.
The elderly man was left badly shaken by the daylight incident but was not hurt.
Officers have appealed to the public for information and have issued a description of a man they want to trace.
He is described as being around 30 and 6ft with a slim build and a grey beard.
He was wearing black trousers, a black top and a woollen tammy hat.
The man was seen running off along a path at the play park on Moncur Crescent, leading to Marryat Street.