Pompey stormed to the top of Southern Group E in the EFL Trophy by producing a blistering second half performance against Gillingham.
A neat finish from Tino Anjorin had given them the lead at Fratton Park, only for Jonny Williams to level just before the break.
But there was no stopping the rampant Blues after the interval and it was one-way traffic from the moment Ben Stevenson restored their advantage.
It was just a question of how many they would score, with Kusini Yengi, Abu Kamara and Ryley Towler all finding the target.
John Mousinho made six changes from the side that beat Port Vale to remain top of League One at the weekend.
A fit-again Yengi led the line after making a cameo appearance in that game, with Gavin Whyte joining him in the forward line.
There were also starts for Ryan Schofield between the sticks, Zak Swanson and Towler in defence, and Anjorin in the engine room.
Josh Oluwayemi and Harry Jewitt-White were allowed to feature on the bench despite currently being out on loan, with academy players Mitch Aston and Koby Mottoh also among the substitutes.
Pompey looked to take control after a slow start and came close to breaking the deadlock on 10 minutes.
Anjorin swapped passes with Kamara and bore down on goal, but could not lift the ball over Glenn Morris.
He did have his first goal for the Blues just a few seconds later, however, courtesy of an inventive finish.
A corner from Jack Sparkes ricocheted towards ANJORIN and he controlled the ball before finding the net with a close-range overhead kick.
But it was not a half full of clear-cut opportunities, with neither side able to find any rhythm going forward.
The visitors did have a chance to hit back, only for a fine sliding block from Swanson to deny Williams a simple finish from Tom Nichols’ centre.
Pompey might have strengthened their lead at the other end, with Towler meeting a deep Sparkes free-kick and drawing a save from Morris.
But Gillingham levelled just before the break, as Nichols beat two defenders in the box before squaring for Williams to slot home.
Half Time: Pompey 1 Gillingham 1
Anjorin did not return for the second half, with Joe Morrell brought on to replace him in the centre of midfield.
Pompey came charging out of the blocks following the restart and retook the lead within five minutes.
It was a fine finish from STEVENSON to open his account, curling the ball home from 25 yards after being teed-up by Whyte.
They almost extended the advantage moments later when Christian Saydee rolled the ball across to Yengi and he thundered a shot against the crossbar.
But YENGI did not have to wait long for a goal, rising highest to powerfully head in a Sparkes free-kick after Kamara had been upended on the left.
It started to calm down a bit after that breathless start and the Australian striker made way for Conor Shaughnessy just past the hour mark.
Swanson and Whyte sent shots off target as the Blues continued to hunt for more goals to put the result beyond doubt.
But it was KAMARA who grabbed the fourth on 72 minutes, receiving a pass from Swanson and curling a fine finish past Morris from the edge of the box.
And it almost got even better, with Morris making a stunning save to stop Sparkes finding the top corner from the left side of the box.
It was only a brief respite for the beleaguered visitors, however, and when Shaughnessy nodded a Sparkes corner towards goal, TOWLER turned the ball home from close range.
That was the cue to bring on forward Mottoh and midfielder Aston, with the latter making his senior debut.
Pompey kept attacking as the minutes ticked away and Gillingham appeared simply relieved to get to the end without any further damage being inflicted.
And they were even denied a consolation when Schofield saved Jayden Clarke's effort in stoppage-time
Pompey (4-2-3-1): Schofield; Swanson, Raggett (c), Towler, Sparkes (Mottoh 81); Anjorin (Morrell 46), Stevenson; Whyte, Saydee (Aston 81), Kamara; Yengi (Shaughnessy 63)
Goals: Anjorin 11, Stevenson 50, Yengi 54, Kamara 72, Towler 80
Booked: Towler
Subs not used: Oluwayemi, Rafferty, Jewitt-White
Gillingham (4-2-3-1): Morris; Orji, Ehmer, Ogie (Masterson 46), Malone (c) (Giles 81); Jefferies (Chambers 85), Clark (Skipper 85); Clarke, Williams, Macarthur; Nichols (Sithole 61)
Goals: Williams 45
Booked: Jefferies, Ogie, Orji
Subs not used: Turner, Gale
Referee: Farai Hallam
Attendance: 5,066 (181 away fans)