It’s the crucial absence of a winning streak which is hampering Pompey’s promotion push.
Paul Cook’s side have 18 matches along with two months and 28 days to break out of League Two automatically.
Yet while time remains on their side, the struggle to string league victories together is applying the brake to their ambition.
Of League Two’s top eight, only the Blues have so far failed to triumph in more than two successive matches.
In comparison, leaders Northampton are presently on a six-game winning run to leave them 16 points ahead of Pompey.
They previously picked up five straight victories until their December encounter with Cook’s men, which yielded a rare defeat.
In total, Chris Wilder’s team have won 11 of their last 12 matches in League Two to reign at the top.
The situation illustrates what Pompey require if they are to succeed in escaping the Football League’s bottom division at the third time of asking.
On three different occasions Cook’s side have clinched back-to-back triumphs, mostly recently against Hartlepool and the Cobblers in December.
Yet they require far longer winning spells if they are to have any realistic hope of breaking into that rock-solid top three.
Plymouth Argyle occupy second spot and have twice embarked on league periods of four consecutive triumphs, last occurring in December/January.
Derek Adams’ side also collected three-in-a-row in August following a 2-1 loss to Pompey at Home Park.
They are presently nine points clear of the play-off spots, although have one win from their last four league fixtures.
Oxford United’s excellent season has already seen them reach the final of the Johnstone’s Paint Trophy, yet promotion remains their overriding target.
Michael Appleton’s third-placed side face Mansfield tonight having won three of their last five league encounters, including beating the Blues.
The U’s have tasted victory in three successive matches on two different occasions so far, underpinning their sustained promotion push.
Pompey’s next opponents – Bristol Rovers – have surged into the play-off frame since winning three-in-a-row in December.
It is a positive run which also occurred in August and then September/October, leaving them fourth in the table, albeit two points ahead of Cook’s side.
Mansfield enter tonight’s Kassam Stadium visit on the back of three successive triumphs.
They achieved a similar tun back in September/October and currently number Morecambe (twice) and Crawley as recent conquests.
Blues followers are well aware Leyton Orient won at Fratton Park on Saturday, yet they began a stuttering season with five consecutive league wins.
Finally, eighth-placed Accrington have played the second fewest matches in League two so far, yet won four-in-a-row in September.
Pompey have games in hand and remain in the play-offs – but desperately need a winning run to truly succeed.