Costly defeat harks back to Cats' low points
This was a performance and a result from Roy Keane's men to send a shiver down the spines of seasoned Sunderland watchers – regardless of how well the Wearsiders played in the opening half hour.
It was reminiscent of the 15-point and 19-point relegation seasons in the way that the Wearsiders somehow contrived to lose a game they should comfortably have won.
And the immediate job of the manager and his coaching staff must now be to ensure that such a match remains an isolated incident.
The hallmark of both those horrific relegation campaigns, in 2002/03 and 2005/06, was how Sunderland would play very well against the best sides and very poorly against the poor sides – rarely losing by more than the odd goal, no matter the opposition.
The common denominator, though, was that the Wearsiders always pegged their performances a notch below their opponents and so, almost always, lost.
If anything, it's a lack-of-confidence thing – taking your lead from your opponents, rather than setting the tone yourselves.
Sunderland outplayed their opponents in the opening half-hour on Saturday, but gradually their standards dropped towards that of an out-of-sorts Portsmouth side and Pompey took advantage of the hosts handing the advantage to them.
The exception for Sunderland was Djibril Cisse, a diamond in the rough of a misfiring side, but a player that the Black Cats have still to get the best out of, despite an impressive record of four goals in eight starts.
No-one is suggesting for a second that the current Sunderland side is not a country mile ahead of those two relegated sides of the past, but similarities existed on Saturday.
And perhaps it is symptomatic of the fact that Keane is now facing – in a much shorter timescale – the tricky problem Peter Reid faced when he tried to take a well-organised Premiership side to the next level by injecting class at the expense of an ultra-committed style.
Bringing star players in will work, provided those star players deliver. At the weekend, as in the previous two games, too few delivered for Sunderland – when the quality ebbed, there was not the energy or the stamina to take up the slack.
Sunderland have now played badly for three games in a row and the bright future which seemed to be promised by the victory over Newcastle United barely a fortnight ago is in danger of looking like a false dawn.
The Portsmouth defeat though was comfortably the worst of the three consecutive losses though, because Tony Adams' men, despite all the star names on their team-sheet, were there for the taking.
They started the game playing with the lack of certainty which you might have expected from a side which had gained just two points from four games and won only once on the road all season, failing to score in their previous three away trips.
And Keane's remodelled side took immediate advantage of Portsmouth's lack of conviction by taking the lead just four minutes in – a perfect way for the Black Cats to end almost 200 minutes of football without a goal.
Sunderland had made five changes to the side which conceded five at Chelsea the previous week, with the back four looking similar to how it had last season – Phil Bardsley coming in at right-back, Danny Collins at left-back.
In midfield, Andy Reid replaced Teemu Tainio, while there was a whole new strikeforce – Cisse and Daryl Murphy coming in for the injured Kenwyne Jones and Martyn Waghorn.
Portsmouth featured two changes – Noe Pamarot coming in, along with the dangerous Niko Kranjcar, who was making his first start of the season – as Papa Bouba Diop and Armand Traore made way.
Sunderland's early lead was provided courtesy of two of Keane's changes – Reid driving a visionary ball forward from the centre of his own half for Cisse to run on to and despatch confidently.
The long ball initially looked as though it was too ambitious, but Cisse's elastic legs carried him swiftly to the ball ahead of floundering marker Sol Campbell and he drove it through David James.
It was not the ideal way for the England keeper to mark his 100th Portsmouth game, but he went on to play a key role in keeping his side in the game.
Before half-time he had palmed a Cisse header over the bar when the Frenchman looked certain to score had he only been able to place his effort either side of the keeper.
James produced a far better stop earlier, flinging himself to his right to push away a low Cisse shot after a breakaway move again carved out by Reid.
Neither of those efforts, though, went as close as livewire Kieran Richardson's effort from 25 yards just after the quarter-hour – his low drive striking the base of James' left-hand post as the keeper stood motionless
In contrast to Sunderland's positive play, Portsmouth were dreadful.
They failed to test Marton Fulop in the opening half and it was hard to find an impressive performance anywhere in the visiting side.
At that point, you could only see one winner.
But Sunderland, who had gone backwards towards the end of the first half – copying Portsmouth's inability to retain possession – failed to get the flying start to the second half that they really needed.
A curious flatness had spread through the game – both on the pitch and in the stands – and within five minutes of the restart, the two sides were on level terms thanks to a fine strike from midfielder Nadir Belhadj which caught Sunderland napping.
The Algerian winger received the ball 30 yards out from Fulop's goal, unmarked, and immediately unleashed a low shot which flew inside the Hungarian's right-hand post, the keeper arriving fractionally too late to reach the ball.
Anyone expecting the goal to spark Sunderland back into life would have been disappointed as Portsmouth carved out two clear openings in the minutes that followed, with their key attacking player, the previously anonymous Jermain Defoe, coming to the fore.
Both shots from the England man flashed wide, but, as the hour approached, Portsmouth signalled they were very much in the game as the tempo picked up.
Sunderland finally upped their game, with Cisse proving a constant threat – at one stage having the ball in the back of the net from a Reid pass – only for the effort to be marginally offside.
But the Black Cats needed more than just the Frenchman to provide a goal threat.
Portsmouth, meanwhile, were finally getting the bit between their teeth and only a brilliant covering tackle from Dean Whitehead stopped Defoe on the edge of the Sunderland area.
In the dying stages, Fulop dived bravely at the feet of Defoe to deny the striker, but, on the stroke of full-time, Sunderland were undone when substitute El-Hadji Diouf lunged in on Glen Johnson as the right-back reached the home penalty area and referee Steve Bennett correctly pointed to the spot.
Portsmouth have proven vulnerable to the late goal this season, but this time it was their turn – 25-year-old Defoe marking his 200th career league appearance with his seventh goal of the season.
I probably saw a different game to most fans, who might have been impressed by Sunderland's first-half domination. But I just didn't see Sunderland as being unlucky not to get anything out of this game.
They had no-one to blame but themselves for they had been lucky enough in the first place to come up against a Portsmouth side which simply didn't turn up for the first 50 minutes.
Sunderland shone in the first half, certainly because they played well enough, but also because Pompey's shocking deficiencies contributed to making them look good.
That the Wearsiders could not take advantage of that, is a cause for concern – as is the way they faded badly, not for the first time this season, in the second 45 minutes.
Portsmouth did not deserve to win on the balance of play, but they did have sufficient quality in their side not to squander every opportunity that came their way.
And Sunderland's expensively-recruited, highly-paid players must look at themselves right now.
They gave their fans a magnificent memory with the victory over Newcastle just a couple of short weeks ago but have failed to perform anyway near the standard expected in the three games that have followed.
Wednesday's Carling Cup tie against Blackburn offers them a quick chance to restore the feel-good factor in the stands, but they need to be forceful rather than fitful.