Kenny Jackett’s men filled their boots with a 6-0 success in the sunshine at Westleigh Park.
A Lee Molyneaux own goal broke the resistance of Lee Bradbury’s side from a corner after 26 minutes.
Then Chaplin took centre stage, tapping in his first finish after 30 minutes from Tareiq Holmes-Dennis’ cross on his Blues bow.
His second, six minutes later, was the pick of the bunch – cutting across the byline and thumping home a left-footed effort.
The striker clinically dispatched a third in first-half stoppage-time to round off his treble.
The goals continued after the break, with Chaplin turning provider for Naismith to tap home.
Sub Curtis Main – one of 10 second-half changes – won a penalty following a foul by Alfie Whittingham after 74 minutes and got up to convert the spot-kick.
Milan Lalkovic nearly rounded off the afternoon with a wonder solo effort with two minutes remaining.
The best of it for Hawks was a first-half chance for Alfie Rutherford which keeper Alex Bass saved smartly from Rory Williams’ through ball.
The only black mark for Pompey was seeing Matt Clarke limp off early on, on an entertaining afternoon which sent the Fratton faithful home happy.