Christian Burgess ensured Pompey returned to winning ways at Leyton Orient.
The defender’s second-half header from a corner put two defeats to bed as Paul Cook’s side picked up their second away maximum of the campaign.
There were a few scares in the first half but the Blues were dominant, particularly after the break, and the margin of victory should have been greater.
The result lifts Pompey to fourth in League Two on 20 points - with a juicy trip to leaders Plymouth up next.
Pompey look to have made the breakthrough after four minutes when Chaplin produced a quality finish from Enda Stevens’ ball, but the flag was up.
Amine Linganzi then should have opened the scoring after 10 minutes when he was left completely unmarked from a corner but headed wide from eight yards out.
There was a let off two minutes later for Pompey when Christian Burgess tangled with Yvan Erichot in the box, but referee Chris Sarginson waved play on.
Cook’s side should have been in front after 17 minutes when Alex Cisak fluffed his clearance to Roberts, who put Chaplin totally free. The teenager should have put the ball away but Cisak kept out his 10-yard effort.
Pompey then looked to have earned a penalty after 30 minutes as Bennett went to ground after tussling with Yvan Erichot.
The ref appeared to have signalled for a spot-kick, but was in fact penalising Bennett for diving and booked the Pompey man.
There was another fierce drive from Chaplin which went wide six minutes before the break.
The only surprise was the game was goalless as the players went in at the interval.
There was another great chance for Chaplin at the start of the second half but he slipped at the vital moment six yards out from Stevens’ centre.
Then there was a let-off for Michael Doyle as he lost out to Alan Dunne, but the sub’s 25-yard chip was held by David Forde at full stretch.
The breakthrough came for Pompey after 58 minutes with a towering header from Burgess at the back stick from Carl Baker’s corner.
Cook’s side continued to get the better of it throughout the second half as they pushed for a killer second.
A string of half chances came their way before Nicky Hunt headed a Baker cross on to his own post with nine minutes left.
The fourth official indicated four minutes of stoppage time after 90 minutes.
But Orient never looked like levelling on Italian Alberto Cavasin’s first game in charge.