Referee Mr Curson stamped his authority on the game in the fifth minute when he booked Gary Holt for a foul.
He was not quite as sharp in the 12th minute in the eyes of Norwich fans when he failed to spot a Portsmouth hand deflecting the ball off Malky Mackay's head in the visitors' penalty area.
There was a close shave for City after 15 minutes when Nigel Quashie's long-range effort from Paul Merson's corner caught the outside of Robert Green's left-hand upright.
Phil Mulryne for Norwich and Quashie for Portsmouth brought saves from the respective keepers and after 30 minutes the Pompey keeper was quickly off his line to deny Mulryne a shooting chance.
The first substitution of the game came in the 54th minute when Neil Emblen, who was making his first start of the season, was replaced by Clint Easton.
A determined run from Holt took him deep into the visitors penalty area but as he crossed the ball it was cleared by a last-ditch interception.
This encouraged the home side but they found the Portsmouth defence in equally determined mood.
Merson brought the save of the game from Green with a fierce angled shot before Svetoslav Todorov made way for Vincent Pericard with 19 minutes left.
Mulryne brought an equally good save from Shaka Hislop but the Pompey keeper was finally beaten by Roberts when the Welsh international got his head to Steen Nedergaard's right-wing cross and the ball flew in at the near post