Berahino stole the show as he marked his first West Brom start with a 36-minute treble to outshine his fellow debutants.
Steve Clarke's side eased into the third round with a professional performance made more eye-catching by the Burundi-born winger's stellar contribution.
The 20-year-old academy product, who fled his war-ravaged home country as a 10-year-old, was by far and away his side's stand-out performer as he took the game to the Welsh side from the first minute to effectively wrap up the win before the half-time whistle had even blown.
Summer signing Scott Sinclair was one of five full debutants for Albion while third-choice goalkeeper Luke Daniels stood in for Ben Foster after he suffered a stress fracture in his foot.
Also making their first Albion starts were defender Diego Lugano and striker Matej Vydra.
Berahino put his side ahead just six minutes in after Sinclair and Vydra combined well.
He doubled his tally 20 minutes later with a lovely drive from the right of the box which left Newport goalkeeper Lenny Pidgeley with no chance.
And he completed the hat-trick from the penalty spot to put the game out of the reach of the Football League newcomers before the half was over.
A tepid second half saw Albion spurn chances through Chris Brunt and Markus Rosenberg as Newport had to settle for a respectable defeat.