Andy Awford was forced to postpone plans to trial a wing-back system in pre-season.
Injuries and unavailability emphatically saw to that during their six summer friendlies.
But, finally, last night the 3-5-2 formation saw the floodlight of day – and Pompey are through to the next round of the Capital One Cup.
Awford elected to roll out the line-up for the visit of last season’s League One play-off semi-finalists Peterborough.
The result was a 1-0 victory and a whole-hearted display which ensured the hosts were worthy of the scoreline.
It was Miles Storey who grabbed the winner in the 12th minute with a superb right-foot shot to mark his full debut for the Blues.
How impressive he looked, too, picking up where he left off with that sparkling cameo at St James Park on Saturday in the league opener.
The Swindon striker was one of six changes in Awford’s side – not that anybody would have realised such was the complete team display which unfolded.
The Posh were dominated in the first half and stepped up their game after the interval without truly breaking through the back three of Ben Chorley, Joe Devera and debutant Paul Robinson.
Certainly, keeper Paul Jones’ evening would have been far too comfortable for Darren Ferguson’s liking as the hosts eased to victory.
Not since 2010 have the Blues reached the second round of the League Cup under its various guises, following defeats to Barnet, Plymouth and Bournemouth.
Now they head into tonight’s draw having seen off opposition from the division above – comfortably at that.
It was an intriguing sight when Awford’s team sheet revealed a 3-5-2 formation, with Alex Wynter and Dan Butler deployed as the wing-backs.
Elsewhere, Nigel Atangana and Storey were rewarded with starts following their excellent impact as substitutes against Exeter at the weekend.
Storey partnered Craig Westcarr in attack as Awford opted to field a twin strike partnership against the Posh.
With the Blues shuffling their bench also, Jed Wallace was among the seven watching on from the sidelines – although there was no space for Jack Whatmough, who caught the eye in the League Two curtain raiser against the Grecians.
Meanwhile, Michael Poke was missing having picked up an injury during training – replaced as substitute keeper by 16-year-old Alex Bass.
It was a promising start from Pompey, who dictated possession in the early moments against their League One opposition.
On 10 minutes, Westcarr almost brilliantly took down a long pass into the box on his chest to create an opening.
Eventually, the ball did fall to Atangana on the edge of the area, whose low drive was dealt with comfortably by keeper Ben Alnwick.
The hosts did take the lead on 12 minutes, though – through a superb strike from Storey.
Butler picked up James Dunne’s pass down the line and fed Westcarr who, in turn, found his strike partner.
Storey then cut across the box and drove a right-foot shot into the far corner to leave the keeper with no chance.
Moments later, Ricardo Santos blocked Atangana’s shot, then Wynter clipped in a cross which Danny Hollands headed goal-wards, only for the keeper to pluck it from under the bar.
Still the Blues pushed and a magnificent cross was swept in by Wynter deep from the right.
The ball’s bounce just eluded the out-stretched foot of Westcarr.
Peterborough staged their first meaningful attack in the 28th minute, when Kyle Vassell found room down the right-hand side of the penalty area, only to see Jones block his shot with his legs.
The visitors were struggling to find a way back and on 32 minutes a wild effort from long range by Kgosi Ntlhe hardly suggested they would.
At the other end, Storey, in particular, was a constant threat with his pace and movement, sparking danger whenever the ball arrived in his vicinity.
Yet it remained 1-0 to Awford’s men when the half-time whistle sounded to end a highly-encouraging opening 45 minutes for the Blues.
Within two minutes of the restart, Vassell went close to grabbing a leveller for the visitors when he rifled a right-foot shot from inside the box which whizzed just over the Blues bar.
It was far brighter by the Posh, who then had Jack Payne drill in an effort which Jones showed safe hands, by diving forward to gather.
Pompey were still having their moments, and Hollands and Dunne combined brilliantly when the former cleverly lobbed the ball into the box and the latter produced a looping header which was saved.
Peterborough had the ball in the net on 55 minutes when Michael Smith’s shot ricocheted kindly into the path of Ntlhe to squeeze past Jones.
However, the linesman cut short celebrations by flagging for offside against the left-back.
Storey, who had already crumpled to the ground with a migraine, was brought off in the 59th minute for Ryan Bird – attracting an ovation in recognition of his excellent showing.
He was soon followed by Wynter, who appeared to have an injury, with Adam Webster asked to operate as right wing-back.
Pompey had a scare in the 70th minute when former player Nathaniel Mendez-Laing got around Butler at the byline – but his inviting cross was hacked away from near the goal-line, while Payne’s follow-up flew over.
It was the hosts’ turn to have a goal ruled out when Westcarr won the ball and finished confidently, only to be called up for handball earlier.
The fourth official indicated six minutes of time added on to provide hope for the visitors, during which Michael Bostwick fired a shot on top of the net.
But Pompey had their win and they are through to the next round following a fine Fratton Park performance.