Gareth Evans and Adam Le Fondre both scored twice as Rotherham overwhelmed Plymouth at Home Park.
Debutant Will Atkinson gave Argyle the lead with a superb shot from 20 yards but that was as good as it got for the home team.
Evans equalised with an angled shot and then grabbed his second after good work from Le Fondre, who was set up for the third by Danny Schofield.
Le Fondre tapped in from close range to complete Argyle's miserable afternoon.
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Plymouth boss Peter Reid told BBC Radio Devon:
"We took the lead but then the wheels came off.
"I think it was a bit of naivety and inexperience, but it's a hard league and we've got to learn.
"I don't think Rotherham worked too hard for their goals and that is disappointing."
Rotherham boss Andy Scott told BBC Radio Sheffield:
"It was an outstanding team performance,
"We changed the system just to make sure that if they did get possesion then they'd have it in the areas that we wanted them too and it worked very well"
"We counter-attacked very well. Bit disappointed with the goal conceded but we reacted extremely well from that."