The female flagged down the victim by the Barley Mow pub near Polegate, East Sussex, before he was suddenly ambushed from behind by a knife-wielding man after getting out of his car to help at about 4.30pm on Sunday.
During the melee, the victim was slashed in the face with a Stanley knife but the attackers fled in a parked car after the innocent man was able to land a punch on the male.
The assailants drove off continuing eastbound in a small black Toyota, possibly an Aygo or a Yaris with an 07 registration. Nothing was stolen from the man.
The 30-year-old victim was treated at the scene by an ambulance crew for a cut to his face.
The male attacker was described as 5' 11", aged in his mid-30s with short scruffy brown hair, clean shaven and was wearing a black hoodie and blue jeans.
The woman was described as being aged in her 20s, 5' 6", slim, with brown hair in a bun and was wearing a red round neck jumper and skinny blue jeans.
Detective sergeant Amanda Hover said: ‘This was a frightening ordeal for the victim who stopped to help a woman who he believed was in distress.
‘We are appealing for witnesses to this incident or information that may help identify the suspects or the vehicle they were driving. This happened at a busy time of day on the A27 and we believe there must be drivers who saw it.
‘We would also like to hear from any motorists who may have dash cam footage of the incident.’
Report online or ring 101 quoting serial 846 of 05/05 if you can help with our investigation.