A goal in each half from the attacking talent, along with headers from Christian Burgess and Marc McNulty, gave the Blues the most comfortable of successes in front of a crowd of 16,670.
Paul Cook’s side were good value for the three points with a controlled and authoritative performance at Fratton Park.
The gap remains five points to the automatic promotion places but it was encouraging to see Pompey respond to their manager’s demand to give fans the conviction they can finish the season in flying fashion.
The game sprung to life after three minutes when referee Michael Bull somehow avoided giving a nailed-on spot kick to Pompey.
Blues fan Haydn Hollis clearly barged Ben Davies over the in the box but Bull waved play on to the anger of the home crowd.
The temperatures were rising early on and the home crowd were making their voices heard.
Paul Jones, back in goal for the first time since September, then had to make a smart save to smother Rob Milsom’s effort.
Michael Smith and Adam McGurk both had chances fly over the top as the pace slowed somewhat.
But the game was reignited a minute before the break with an inspired effort from Bennett.
He steamed past Elliott Hewitt down the left before cutting across the byline and firing through Scott Loach.
Pompey should have had a second two minutes after the restart but McGurk somehow put his header wide from Davies’ free-kick.
It didn’t matter after 49 minutes as Bennett had his second as he coolly slotted past Loach after being classily freed by Roberts.
That made it a comfortable afternoon for Cook’s side, as they cruised to the win.
Jones did drop a cross from Curtis Thompson with 30 minutes left which Jon Stead somehow failed to force home.
Pompey were in the ascendancy, though, and settled it with nine minutes left with Burgess’ bullet header from Enda Stevens’ free-kick.
And there was still time for substitute McNulty to nod in a fourth from Davies’ free-kick in stoppage-time.
That ensured there were cheers on the final whistle as the home crowd showed their appreciation for a dominant display.