Jayden Stockley fired Pompey to the top of League Two as they picked up a 2-1 win at Bristol Rovers.
Paul Cook’s side equalled the Blues’ best start to a season in 13 years as Gareth Evans got the other goal against the Gas.
Stockley wasn’t even named in the starting XI but a injury to Adam McGurk in the warm-up gave the loanee the platform to win the game.
Evans put Pompey in front after 29 minutes with a smart header, before an unfortunate own goal from Aaron McCarey on his debut levelled it up three minutes after the break.
But then up stepped Stockley to settle it after 71 minutes and send the Blues top.
It was an even start to the clash on a sunny afternoon at the Memorial Ground.
The game sprang to life after 15 minutes when Evans jinked clear of a series of challenges but was unable to beat Lee Nicholls with his finish.
Conor Chaplin was given a let off four minutes later when he somehow put a free header wide from two yards - but the offside flag was up.
Pompey made the breakthrough after 29 minutes when a peach of a cross from Bennett was deftly headed home by Evans.
Aaron McCarey was called into action to make a couple of smart stops as he kept out a deflected cross from Lee Brown.
The Irishman was then equal to Jermaine Easter’s drive as Rovers found some impetus.
Evans then fired a first-time effort at Nicholls from Chaplin’s pass as Pompey finished the half on the front foot.
Rovers were back in the game three minutes after the restart with a fortuitous leveller.
Daniel Leadbitter’s cross was met by Easter whose shot cannoned off the bar and hit McCarey before trickling over the line.
There was a let off for Pompey after 58 minutes when Easter’s shot came back off the post from 30 yards with the aid of a deflection.
Chaplin looked to have a decent appeal for a penalty seconds later but the ref said there was no foul from Tom Parkes and booked the teenager for diving.
Bennett then went clean through after 67 minutes but fired a fine chance wide when he should have done better.
That didn’t matter four minutes later, though, as Stockley fired Pompey into the lead as he volleyed home Davies’ pinpoint delivery.
Pompey then looked comfortable as they saw out the finale to grab another three points on the road.