Romaine Mundle's goal was only his second since joining Sunderland last summer
Midfielder Alan Browne scored his first goal for Sunderland as they won at Portsmouth to maintain their 100% winning start to the Championship season.
The Republic of Ireland international toe-poked home from close range six minutes into the second half after Zak Swanson's unfortunate own goal had given them the lead before half-time.
Romaine Mundle soon added a third to end any hopes of a comeback by last season's League One champions.
An own goal by Luke O'Nien provided Portsmouth with a late consolation, but having drawn their first three games, they are still searching for their first win in the second tier of English football since April 2012.
Sunderland did not have any of their four deadline-day signings in the matchday squad, but Pompey included Ibane Bowat, Mark O’Mahony and Freddie Potts on the bench, the trio having been brought in by boss John Mousinho in the last week.
There was little of note at either end in the first half hour, though Pompey’s Connor Ogilvia saw a header saved from Matt Ritchie’s cross and Patrick Roberts fired a shot wide for Sunderland after cutting inside.
But the game turned when Will Norris saved from Eliezer Mayenda, as Jordan Williams' clearance cannoned off team-mate Swanson and into the net.
It was a body blow for Pompey and the best they could muster in response before the interval was a Ritchie shot that Anthony Patterson saved.
Whatever plans Mousinho put in place at half-time with a view to getting back on level terms were left in ruins within 10 minutes of the restart.
Roberts surged into the box before cutting a great ball back to Mayenda, who miscued but the alert Browne – signed by Sunderland after leaving Preston – managed to guide it over the line, although he was lying on his back at the time.
Mayenda was involved again as he carried the ball forwards from his own half before feeding Mundle, who beat Norris at his near post with a left-foot shot.
Pompey made four changes at the hour mark - O'Mahony was the only one of their three new faces introduced - but had only managed one shot on target when Swanson nodded back across goal at the far post and O’Nien, diving to try to clear, headed it into his own net.
The beaten hosts will now look to regroup over the international break ahead of a tough September when they face West Brom and Sheffield United at home, either side of a trip to Burnley.
Portsmouth boss John Mousinho told BBC Radio Solent:
"Sunderland thoroughly deserved to win and I’m disappointed to lose the game.
"There was only very small margins in it I thought, we played quite well up until the goal but there were small bits in the second half we didn’t get quite right.
"You get punished by good sides like this, I think there was lots of small moments that once added up created a gulf between the two sides, it’s nothing I don’t think we can bridge at some point but we have to be better than that."
Sunderland boss Regis le Bris told BBC Radio Newcastle:
"We are happy for sure because it was a tough game and I think the game plan was good but it’s not always easy to apply.
"I don’t know if we are a team who wants to control the game, who wants to create chances, who wants to create an unbalance in the opponents defence. This part of the game is not our best.
"I’m not sure we want to be the kind of team that has twenty, thirty or more passes. In the first-half, this wasn’t so clear.
"I think away especially, the solution is in the defence. If you are able to attract the opponent, recover the ball and then fast attack and counter-attack after that, it’s the best way to score I think."
