The sure touch that has helped seal a leaky Leeds defence deserted Andy O'Brien at the worst moment as Simon Grayson's promotion-chasers threw away a two-goal lead at Elland Road.
Manager Grayson took O'Brien on loan from Bolton two months ago in direct response to defensive failings that cost his side five goals at Barnsley, six at home to Preston and four against Cardiff.
It looked a shrewd move as he launched his stay with a 4-1 win at Scunthorpe that began an undefeated run which saw Leeds emerge as genuine contenders for a belated return to the Barclays Premier League.
The sequence stands at 11 games after this pulsating 3-3 draw, but O'Brien, 31, looked inconsolable after turning Nadir Ciftci's innocuous cross past goalkeeper Kasper Schmeichel with seconds remaining.
At least it did nothing to jeopardise a proposed £250,000 permanent transfer next month. Grayson even absolved his player from blame, saying: 'It was frustrating to drop a couple of points after being two goals ahead on two occasions and individual mistakes made it even harder to take.
'It was a lack of communication for their third goal and, if anything, I thought it was probably down to Kasper to make the call, as he was leaving his line.
'The manner of that goal was hugely disappointing, but Andy played really well once more and Kasper made one or two top saves. There is still a great belief in the dressing room that we can reach the Premier League.'
Leeds were cruising after Max Gradel bundled home a Paul Connolly cross in the seventh minute and Jonny Howson sidestepped two challenges before expertly curling a shot beyond Jamie Ashdown three minutes later.
Neat finish: Max Gradel scores the opening goal for Leeds at Elland Road
Leeds v Portsmouth Leeds: Schmeichel, Connolly, O'Brien, Collins, McCartney, Snodgrass, Howson, Johnson, Gradel (Sam 81), McCormack, Paynter (Becchio 65). Subs Not Used: Higgs, Bruce, Kilkenny, Hughes, Somma. Booked: McCartney, Schmeichel. Goals: Gradel 7, Howson 10, Johnson 62.
Portsmouth: Ashdown, Halford, Mokoena, Rocha (Sonko 60), Dickinson, Nugent, Ward (Kanu 59), Mullins, Hughes, Utaka (Ciftci 88), Kitson. Subs Not Used: Flahavan, Hreidarsson. Booked: Mokoena, Kitson. Goals: Nugent 33, O'Brien 63 og, 90 og. Att: 31,556 Ref: David Webb (County Durham).
That should have banished any misgivings from the way a two-goal lead was surrendered at Leicester two days earlier. Instead, David Nugent set Leeds' nerves jangling with an England-class finish into the top corner in the 33rd minute.
An unstoppable Bradley Johnson volley from a half-cleared corner should have removed any unease in the 62nd minute but a familiar edginess at the back reappeared within a minute as Richard Hughes' shot deflected off O'Brien and left Schmeichel wrong-footed.
Grayson was convinced Leeds should have had a penalty when Ross McCormack was upended and his sense of injustice was hardly helped in the final minute when O'Brien stretched for Ciftci's low cross and diverted it past Schmeichel.
Both managers were scathing about Durham referee David Ward. Portsmouth boss Steve Cotterill said: 'Good luck to him, and I hope he goes on to have a good career. But I have never heard of him before and I would like to bet there were more experienced referees controlling games in front of a handful of people while this fella is trying to handle an occasion like this in front of 33,000. That can't be right.'
Grayson was just as unhappy, saying: 'Our fans are very knowledgeable, and they don't give the referee the sort of stick he got unless it is for a very good reason.
'Experience has a lot to do with the way two-goal leads have slipped away in our last two games but I still feel the positives far outweigh the negatives.'
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Explore more:People: Simon Grayson, David Nugent, Jamie Ashdown Places: Leeds, Cardiff