It wasn’t merely victory which was crucial as Pompey capitalised on one of their games in hand.
The identify of the opposition was also heartening, a 3-2 success arriving against Rotherham in last night’s Fratton Park encounter.
The Millers headed into the fixture positioned fourth in League One - and the Blues suddenly had a rare top-six scalp.
The lack of victories over high-flying opposition has been a constant criticism of Kenny Jackett’s side throughout 2019.
Yesterday evening they laid down a vital marker. In the process, the Blues climbed to 10th to position themselves within two points of the play-off spots.
There have been plenty of calls for Jackett’s head this season, yet presently Pompey are undefeated in seven in all competitions - and suffered one loss in their past 12.
Had it not been for a period which shipped a flurry of last-gasp goals, their placing would currently be considerably loftier.
Still, Jackett’s men are building momentum rather encouragingly and the resurrected Ronan Curtis was among the thick of their latest win.
The Irishman netted after just 33 seconds, representing his fifth goal in six outings, and he was instrumental in the subsequent 3-2 scoreline.
The Blues took the lead three times during the match’s duration, with Marquis grabbing the second, but finally it was Ben Close’s 66th-minute strike which proved decisive.
How the midfielder enjoyed that moment in front of the Fratton end - and the hosts kicked off the first of six games out of seven at Fratton Park with an important three points.
Jackett unsurprisingly had retained the same XI which collected a 3-0 win at Rochdale on Saturday.
It also marked an unchanged match-day squad of 18, with the substitutes’ bench not altered for the visit of the high-flying Millers.
With Tom Naylor still sidelined by a hamstring injury, Lee Brown continued to captain the side in his absence, with Anton Walkes once again deputising in a midfield holding role.
Elsewhere, Oli Hawkins was handed successive outings at centre-half alongside Christian Burgess, with Sean Raggett injured and Paul Downing out of favour.
Meanwhile, Jack Whatmough is not yet under consideration during his progress following long-term injury, while Bryn Morris’ injury frustration drags on.
When the match got underway, it took just 33 seconds for the Blues to register, inevitably through the man-of-the-moment Curtis.
Ryan Williams produced a sublime diagonal pass from the right into the Irishman’s path down the left to set him away.
Curtis then cut in from the right and, outside the box, produced a wonderful right-footed finish into the far top corner of the net to break the deadlock in style.
The excellent start could have been further enhanced on eight minutes when Brandon Haunstrup cleverly dinked the ball into the penalty area left footed.
It was designed for the run of Close, who couldn’t quite reach ahead of keeper Daniel Iversen, who ended up fumbling before finally collecting.
At the other end, Craig MacGillivray was drawn into a superb stop, diving to his left to take, Kyle Vassell’s powerful effort from the edge of the area which had initially gone through Hawkins’ legs.
Rotherham levelled on 15 minutes, stemming from a free-kick delivered from 25 yards by Vassell.
The striker drilled a low shot which comfortably navigated the wall and, when parried by MacGillivray, Ladapo was there to pounce from close range and capitalise.
Moments later, Carlton Morris delivered a deep cross from the right and Trevor Clarke headed over at the far post when perhaps a taller player could have netted.
Rotherham continued to threaten and, on 27 minutes, a ball down the left channel sparked another attack, with MacGillivray foiling Ladapo’s subsequent close-range shot.
Referee Antony Coggins was beginning to try the patience of the Fratton faithful, who had become frustrated by his display, finally bursting into a chant of ‘You’re not fit to referee’.
Close should have restored the Blues’ lead on 35 minutes, when a cross from the left was headed back by Ellis Harrison at the far post.
How the midfielder’s eyes must have lit up, but instead he blazed a fierce right-footed shot comfortably over the bar from 12 yards out.
However, it was 2-1 to Pompey on 37 minutes, with Marquis the scorer.
Brown clipped in a cross from the left and Harris planted a header which appeared on target, only for Marquis to divert it in from close range through his head.
During two minutes of first-half stoppage time, Marquis had a golden opportunity to grab his second, but instead wasted the moment.
Curtis delivered a right-footed cross from the left and the striker, with no-one around him and just the keeper to beat, meekly headed it straight at Iversen.
With Harrison also lurking behind him and no sign of an off-side flag, he should have done far better as the Blues headed into the interval with a 2-1 lead.
Rotherham made a change at the break with Chiedozie Ogbene introduced for Matt Olosunde, coming on at left-back, with Billy Jones to right-back, presumably to shut the door on the dominant left-sided partnership of Brown and Curtis.
Pompey had the ball in the net once more of 47 minutes, but Harrison was rightly ruled to have fouled the keeper as he rose to bundle it over the line.
The striker was then booked for a lunge on Jones, which required the full-back to receive treatment.
Rotherham levelled on 62 minutes through a penalty the Blues can have no arguments with being awarded.
Morris cleverly spun Hawkins, whose outstretched foot took the winger down for a spot kick which Ladapo comfortably converted to make it 2-2.
Within four minutes and Jackett’s side were once more in front, this time Close getting himself on the scoresheet.
Curtis delivered a corner from the left and, with the Millers struggling to clear, Close popped up on the edge of the area to take it on the chest and then connect with a right-footed shot, which found the far bottom corner.
Rotherham made a double substitution on 73 minutes, using up their full quota of replacements, only for Jones to go off injury a minute later, reducing them to 10-men.
Not that the numerical disadvantage told in the visitors’ play, but Pompey had enough to hold on and claim a crucial victory.