A man walked up to a 62-year-old woman and punched her in the face, splitting her lip.
Police believe the offender may be the same man who three hours earlier indecently assaulted a 68-year-old woman.
The punch attack happened at about 10.15pm on Saturday in Chailey Avenue, Rottingdean, Brighton.
Detective Inspector Paul Fullwood said: "The victim was minding her own business as the man walked towards her, attacked her and casually walked away."
At 7.40pm the same evening a man sexually assaulted a pensioner in The Twitten which links Steyning Road and Marine Drive, Rottingdean.
Mr Fullwood appealed for witnesses or anyone with information about either attack to call Brighton CID on 0845 6070999.
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