Berahino was handed his first start for West Brom in the Capital One Cup second-round tie and marked the occasion by scoring three times inside the opening 37 minutes.
The 20-year-old academy product, who with his family left the war-ravaged African state of Burundi as a 10-year-old, was by far and away his side's stand-out performer.
"He was excellent, really great," said the Albion head coach on the day Berahino was named in the England Under-21 squad for their forthcoming qualifiers.
"I'm really pleased for him because he was at Peterborough last year where he did ever so well in the Championship but then got a really nasty injury which kept him out for seven months.
"But he worked hard over the summer with the medical staff and got in great shape. He joined us for pre-season and I can't say I'm surprised by how well he's done. He's been really good in games and done well for us.
"I'm absolutely delighted for the boy because he's worked so hard for his chance and he took it with both hands.
"You saw his performance. In the first half he was the best player on the pitch. He tired a bit in the second half - as did a few others who haven't had much playing time recently.
"But he's given me a lot to think about and I'm really pleased he has."
Newport manager Justin Edinburgh was justifiably upbeat about his side's performance.
"I think we were a bit disappointed to come off 3-0 down at half-time," said the former Tottenham player.
"We started brightly and found good rhythm but I think we knew we had come up against Premier League class. They're so clinical, they had three shots on target and three goals.
"I'm a proud man. I thought the players acquitted themselves well right to the end and the fans were excellent too, as the game wore on they got louder.
"We had nothing to lose and all to gain but we take a lot of credit. We've not done ourselves any harm, that's for sure."