Police officers in Patong were called to deal with the situation when the argument took place about 12.35am last Wednesday, close to the Taipan nightclub in Rat-U-Tit 200 Pi Road, near the intersection with Patong's Soi Bangla walking street.
The Australians had been drinking and the cause of the argument remains unclear.
The couple were taken with their friends to Patong Hospital where the injured woman declined treatment, an officer at Kathu Police Station, which oversees Patong, said today.
The woman who assaulted the tourists was fined 500 baht at the police station.
Police in Patong said a tuk-tuk driver and an American had a disagreement in Patong last night and came to blows. Neither was seriously injured.